Table of Content

10 June 2022, Volume 44 Issue 3

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A Special Issue of Efficient Development Technologies for Tight Sandstone Gas Reservoirs in Western Sichuan

Key Technologies and Prospects of Stable Production of Jurassic Tight Sandstone Gas Reservoirs in Western Sichuan

GUO Tonglou

2022, 44(3):  1-11.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.02

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The characters of tight sandstone gas reservoir types in the Western Sichuan Depression were complex, such as complicated channel sand stacking, unstable the sand body distribution, low reserve taste, complex gas-water relationship, low natural productivity, poor stable production capacity, and low recoverable reserves in a single well. In order to achieve continuous production increase and stable production of gas reservoirs, based on the reprocessing and interpretation of old seismic data, a complete geophysical and logging fine evaluation technology system was established, which achieved fine characterization of channel sandstone, accurate reservoir prediction and water saturation and quantitative evaluation. Aiming to increase production, we selected double geological and engineering sweet spots and formed a mixed well pattern plus large-scale multi-stage and multi-cluster volume fracturing reservoir stimulation technology system, of which the type was the combination of linear, "Y" "X" "V" etc on the plane, and "multiple wells in one field and multiple layers in one well" with well type group optimization in vertical direction. The construction displacement was increased from 5$\sim$8 m$^3$/min to 16$\sim$18 m$^3$/min, and the sand addition intensity was increased from 0.4$\sim$0.7 t/m to 4.0$\sim$4.5 t/m, the number of fractures increased from 20$\sim$30 clusters to 50$\sim$80 clusters, and the single-well productivity increased from 5.07$\times$10$^4$ m$^3$/d to 15.64$\times$10$^4$ m$^3$/d. Taking seismic-eology-modeling-mathematical modeling-engineering-economic integration as means, the origin and scale of remaining gas were found out, and measures such as infill adjustment, layer transfer, sidetracking, repeated reconstruction and process maintenance were put forward to improve the gas reservoir recovery rate. It has achieved continuous and stable production of more than 2 billion cubic meters of tight sandston gas reservoirs in western Sichuan for 18 years. With the popularization and application of these technologies, the Southwest Oil and Gas Company$'$s annual production of tight natural gas is expected to remain above 3 billion cubic meters during the "14th Five-Year Plan" period, and the production will continue to be stable.

Integrated Sweets Spots Evaluation Technology for Tight Sandstone Gas Reservoirs in Zhongjiang Gas Field

LIU Yan

2022, 44(3):  12-25.  DOI: 10.11885/j.issn.1674-5086.2022.01.27.03

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The gas reservoir of Shaximiao Formation in Zhongjiang Gas Field has a structural pattern of two depressions surrounded by three uplifts. The three uplift area in the high structure part has been developed efficiently, but the evaluation technology of the channel sweet in spot two depressive structural low areas needs further study. Aiming at the problem that the existing geological sweet spot study focuses on reservoir quality evaluation, but the gas prediction depends on seismic interpretation and has strong multi-solution, the technology of geological sweet spot prediction with higher accuracy is formed by combining reservoir formation and seismic research. Based on the evaluation of geological sweet spots, engineering sweet spots evaluation, which is used to evaluate the adaptability of hydraulic fracturing technology, is conducted firstly. Then, taking on the research of the differential accumulation of deep-source and shallow-gathering secondary gas reservoirs, the integrated sweet spot prediction technology is established by taking both geological sweet spot and engineering sweet spot into consideration. And combining the new fracturing technology, the limit of conventional reservoirs of geological sweet spots can be lower, the rate of gas well can be significantly increased, thereby the two depressive area can be developed effectively. The integrated sweet spot prediction technology can be used to evaluate low quality rivers which is more suitable for the new fracturing technology, so the rivers in lower structural areas and with more poor physical properties can be developed.

The Techniques of 3D Joint Channel Sandstone Processing in Xinchang-Shifang Area Western Sichuan

MA Zhaojun, LIU Hongai, LING Hang

2022, 44(3):  26-36.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.01

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The medium shallow layer channel sandstone in Western Sichuan is thin in thickness and narrow in width, so it is very difficult to identify by seismic data. It is the premise for seismic technology to identify sand body distribution to keep the relative change relationship between seismic reflection amplitude and waveform. Because of the large time span of acquisition, different acquisition instruments and different geometry, there are some inconsistencies among the data in Xinchang-Shifang Area, such as system time difference, amplitude, frequency and waveform. Based on the analysis of the original data, the problems and difficulties in the target processing of the 3D joint channel sandstone are clarified, and a set of solutions and ideas are established. The purpose of data processing is to improve the imaging effect of middle and shallow layers and to highlight the seismic response characteristics of channel sandstone. It mainly studies, tests and analyzes the technologies of time difference correction, denoising, static correction, amplitude recovery and compensation, deconvolution, surface consistency processing, residual static correction, data regularization, velocity analysis, migration imaging and gather optimization, and completes the actual data processing. The processing results have the characteristics of high signal-to-noise ratio, high resolution and high fidelity. The wave groups between blocks have good continuity, stability and consistency, which can provide high-quality basic data for subsequent structural interpretation, sand body characterization, reservoir prediction and gas bearing identification.

Dim Spot Channel Sandstone Identification for Tight Sandstone Gas Reservoir in Western Sichuan

WANG Jian, DUAN Wenshen, BI Youyi

2022, 44(3):  37-46.  DOI: 10.11885/j.issn.1674-5086.2022.01.25.01

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The Shaximiao Formation gas reservoir in the eastern slope belt of Western Sichuan Depression is a low-permeability tight channel sandstone gas reservoir. Most channels show "bright spot" reflection characteristics of strong trough amplitude and low impedance on seismic profile. With the development and evaluation of this gas reservoir, it is found that some wells drilled in the channel sand body in the non-target zone also have good hydrocarbon display. However, these channels have the feature of "medium and weak trough amplitude" in the post-stack seismic data, resulting in unclear shape, poor continuity and difficulty in identifying the channels on the plane attribute of seismic amplitude, which is called "dim spot" channel sandstone. Based on the formation mechanism of "dim spot" channel sandstone, the forward modelling analysis is carried out, and it is confirmed that the poor physical property is the key factor for the formation of "dim spot" channel sandstone; then, by analyzing the AVO characteristics of gather, it is clear that the "dim spot" channel has the characteristics of Class I or Class II$_{\rm a}$ AVO characteristics in the prestack gather; finally, the problem of "dim spot" channel sandstone identification is solved by using partial stack technique of dominant incident angle. The feasibility and effectiveness of this method are verified by actual drilling, which strongly promotes the efficient evaluation and production of this gas reservoir.

Gas and Water Distribution and Main Controlling Factors of Tight Sandstone Gas Reservoir in Shaximiao Formation, Zhongjiang

XIONG Liang, HENG Yong

2022, 44(3):  47-58.  DOI: 10.11885/j.issn.1674-5086.2022.01.27.02

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In order to clarify the gas-water distribution law and main controlling factors of Shaximiao Formation deep source shallow accumulation tight sandstone gas reservoir in Zhongjiang. Based on the data of core analysis, well logging, gas test, production, nuclear magnetic resonance and formation water chemical analysis, the microscopic occurrence state, macroscopic distribution law and main controlling factors of formation water are studied. The results show that the formation water salinity of Shaximiao Formation is CaCl$_2$ type III$\sim$V, and the formation water exists in the reservoir in the form of bound water and capillary water. The distribution of gas and water is controlled by faults, local structures and internal heterogeneity of channels. Fault is not only the basis of gas charging, but also the passage of loss, which controls the macroscopic distribution characteristics of gas and water. Fractures develop in the near fault layer, and natural gas is dispersed during gas reservoir adjustment. Gas-water cobedding is dominant in channel near fault. The local distribution characteristics of gas and water are controlled by the heterogeneity and local structure in the channel. The lithologic (physical) sealing developed in the channel can prevent the migration and loss of natural gas to the high fault layer, and make the gas and water distribution in the sausage type, while the gas layer is developed in the lower part of the structure. The distribution pattern of gas and water in the channel without lithologic sealing is "upper gas and water", the high part of local structure is gas layer, and the lower part of structure is water layer or gas and water layer.

Logging Evaluation Technology of Tight Sandstone Gas Reservoir in Western Sichuan and Its Development Prospect

LIU Chengchuan, CHEN Jun, CHENG Hongliang

2022, 44(3):  59-69.  DOI: 10.11885/j.issn.1674-5086.2022.01.25.03

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Tight sandstone gas reservoirs in western Sichuan have the geological characteristics of low porosity, low permeability, diverse pore structure, and complex gas-water relationship, which makes the parameters such as porosity, permeability and water saturation obtained by traditional logging evaluation technology with low accuracy. Well evaluation is prone to bias, so it is urgent to carry out research on targeted well logging evaluation technology. This paper takes the complex channel tight sandstone gas reservoir in the Shaximiao Formation in the Zhongjiang River as the research object, and combines the exploration and development practice of gas reservoirs. Based on the standardization of logging curves based on sedimentary microfacies constraints, multiple regression, BP neural network, flow-based reservoir physical property evaluation technology of the unit and the multi-factor intersection, the fluid identification radar map based on multi-factor discrimination, and the saturation evaluation model with variable $m$ and $n$ parameters are the core of the tight sandstone gas reservoir logging evaluation technology system, which is Zhongjiang Shaximiao. It provides strong support for the efficient development of gas reservoirs. The formed logging evaluation technology system for tight sandstone gas reservoirs provides an effective reference for related research on the same type of gas reservoirs.

Pore Structure Characteristics of Tight Sandstone Reservoir and Its Influence on Development

ZHAN Guowei, GU Zhanyu, PANG Heqing, CAI Zuohua

2022, 44(3):  70-84.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.07

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The pore structure characteristics of tight sandstone are the core research work of tight oil and gas geological evaluation. Through a variety of experimental analysis methods such as cast thin section, X-ray diffraction, scanning electron microscope, conventional mercury injection, constant velocity mercury injection and gas-water relative permeability, the pore structure characteristics of dense sandstone of Shaximiao Formation in Zhongjiang Gas Field, Western Sichuan are studied, the causes of pore structure differences are discussed, and the influence of pore structure on development is analyzed. The research shows that the tight reservoir rocks of Shaximiao Formation in Zhongjiang Gas Field are lithic arkose, feldspathic lithic sandstone and lithic sandstone; the physical properties of the reservoir are affected by the combination of primary minerals, diagenetic evolution process and their products. The contribution of quartz to the permeability of the reservoir is relatively obvious, but not obvious to the porosity. Clay minerals and calcite have obvious effects on the porosity and permeability, which are negatively correlated; among the pore structure parameters, the pore throat combination relationship and the size of roar determine the reservoir permeability, and the large pore throat contributes the most to the reservoir permeability; pore structure has an obvious impact on productivity and gas well production characteristics. The better the homogeneity of pore structure, the higher the corresponding gas well productivity and average daily gas production. The research results have important theoretical significance for deeply understanding the pore structure of tight sandstone and the difference of gas well development effect, and can provide scientific basis for reasonable development and evaluation of gas reservoir.

Research of Production Decline Model Dominated by Late-boundary Flow for Tight Gas Reservoir Under a Constant Flowing Pressure

ZHAN Zedong, DENG Weifei, YAN Huanrong, YAN Xuemei

2022, 44(3):  85-92.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.06

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To study production decline model dominated by late-boundary flow for constant volume tight gas reservoir, and to provide a theoretical basis for gas reservoir performance analysis and index prediction. Based on experimental results of seepage mechanism for tight gas reservoir, after analyzing and establishing the seepage differential equation of tight gas reservoir, focusing on the late stage of boundary flow of constant volume tight gas reservoir, combined with material balance equation, a new equation and its differential equation were both proposed for the gas production vs time, and based on which, the quantitative model of initial decline rate and geological factors was determined. The results show that:(1) compared with conventional gas reservoirs, the non-Darcy flow pressure loss in tight gas reservoirs consists of three parts, which are derived from fluid internal friction, turbulence effect and start-up pressure, which is also an important reason for the anomaly of binomial productivity equation. (2) Because of turbulence effect and start-up pressure, Arps$'$s decline model was not followed for gas wells of constant volume tight gas reservoir, and the existence of start-up pressure gradient and the turbulence effect slows down the production decline rate of gas wells, and the gas well production decline model follows exponential decline, only when the turbulence coefficient tends to 0, without start-up pressure gradient, and the pseudo time is used instead of time. (3) The example shows that the binomial productivity anomaly can be effectively eliminated by introducing the start-up pressure term, and the reservoir parameters such as gas well dynamic reserves and start-up pressure gradient can be calculated by using the new model, which lays a theoretical foundation for the analysis of main controlling factors of production decline, formation parameter inversion and dynamic index calculation of constant volume tight gas reservoir, abnormal treatment of binomial equation in tight gas reservoir included, so it has strong practicability and foresight.

Quantitative Evaluation for Development Potential of Remaining Gas in Tight Sandstone Gas Reservoirs

ZENG Yan, CAO Tingkuan, GAO Wei

2022, 44(3):  93-101.  DOI: 10.11885/j.issn.1674-5086.2022.01.25.02

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The distribution of remaining gas in tight sandstone gas reservoir is complex, and it is difficult to quantitatively evaluate the development potential, which restricts the development and adjustment of gas reservoir at the middle and late stage. Aiming at problem of quantitative characterization of remaining gas, taking Js2 gas reservoir in Xinchang Gas Field as an example, comprehensive numerical simulation and actual encryption adjustment well development effect and economy, the factors affecting the remaining gas potential are formation pressure, reserve abundance and permeability in descending order. The remaining gas potential index is defined to comprehensively consider the contribution of the above factors to the economically recoverable reserves of infill wells in the remaining gas areas. Then, the mathematical expression which can be used to describing the relationship between remaining gas potential index and economic recoverable reserves of infilled horizontal wells is established. So, the quantitative characterization of the development potential for remaining gas is realized. For Js2 gas reservoir in Xinchang Gas Field, case analysis shows that horizontal wells can be used to infill the areas if the remaining gas development potential index of is greater than 0.7. Accordingly, one favorable area is selected in the northeast of J$s_2^4$ gas layer, and the reserve of the remaining gas area with high water cut in the edge is effectively utilized by infilling a horizontal well. The quantitative evaluation method for remaining gas is verified by the production of the infilling horizontalwell.

A New Evaluation Method for Potential of Development Benefit of Xinchang Penglaizhen Formation Low Permeability Tight Sandstone Gas Reservoir

LIU Lu, DUAN Yongming, ZOU Chenrong

2022, 44(3):  102-109.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.04

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Xinchang Penglaizhen Formation gas reservoir is a typical low permeability tight sandstone gas reservoir with the earliest development and highest recovery in Southwest Petroleum Branch, SINOPEC. The gas reservoir has entered the later stage of development, it is difficult to enhance gas recovery and economic benefits, because it has low formation pressure and low abundance of remaining reserves. In order to ensure the sustainable development of gas reservoirs, it is necessary to evaluate the potential of gas reservoir development quantitatively. By means of analog integrated modeling and with the economic and technological evaluation at the core, We carried out the multi-factor sensitivity analysis of gas reservoir recovery, and studied the lowest reserve abundance for different well types under different gas prices, different internal rates of return and different formation pressures. The evaluation model of benefit development potential of Xinchang JP gas reservoir was established to evaluate gas reservoir potential at any development stage and under different economic policies. The efficiency development potential evaluation model has high accuracy, and the coincidence rate with the actual deployment well economic benefit is 88%, and the net profit is 10.87 million yuan.

Enhanced Gas Recovery Technology for Large High-stack Tight Sandstone Gas Reservoirs

LI Huachang, LI Huaji, LI Feng, XU Xin

2022, 44(3):  110-120.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.03

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The formation of Shaximiao gas reservoir in Xinchang Gas Field is tight, with ultra-low permeability, low porosity, and extremely low in natural productivity. It is mainly developed through artificial fracturing. By systematically analyzing the main factors affecting the gas reservoir recovery, a comprehensive technology was formed, which was based on the fine description and classification evaluation of the gas reservoir. The core was based on the distribution law of residual gas of the quantitative evaluation with the integration of modeling and simulation and the evaluation of the development potential of residual reserves constrained by profit. And the means was three-dimensional development of well pattern and optimization of differentiated countermeasures. The research results showed that it had limitation for tight sandstone gas reservoirs to rely on a single technology to improve the recovery factor, and the joint research of multiple technologies could maximize the recovery factor and effectively increase the recovery factor of the Shaximiao Formation gas reservoir by 31.71%. Multiple rounds of fine gas reservoir descriptions had laid the foundation for the selection of strategies for enhanced gas recovery, and the error rate of recalculated reserves was less than 2%. Quantitative description and potential evaluation of remaining gas provided a reliable guarantee for infill adjustment and benefit development of gas reservoirs, clarify the types of remaining gas in gas reservoirs and their benefit development limits, and he recovery was increased by 8.28%. The three-dimensional development and differentiated development strategies of multi-layer mixed well pattern were the main means to achieve enhanced gas recovery in gas reservoirs, and the recovery was enhanced by 23.43%.

Development Effect Analysis of Tight Gas Reservoir Considering Differential Relative Permeability

WANG Yongfei, FANG Quantang

2022, 44(3):  121-130.  DOI: 10.11885/j.issn.1674-5086.2022.02.16.02

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Fracturing is an important measure to increase production of low-permeability tight gas reservoir, and gas reservoir development performance prediction considering geological engineering integration is a hot issue in tight gas reservoir development. Large scale hydraulic fracturing will also lead to the difference of phase permeability between the reformed area and the unmodified area, and different reservoir types also correspond to different phase permeability relationships. Therefore, the integrated simulation of tight gas reservoir based differential on dissimilatory relative permeability is of great significance. This paper starts with the engineering geological integrated modeling process, introduces the differential relative permeability embedding method, and combines the three types of reservoir geology and relative permeability relationship to form a simulation process considering differential relative permeability. This simulation method can effectively solve the problem of poor fitting effect of water production in the early flowback stage. Through the simulation considering differential relative permeability, the development characteristics and development effects of three types of low-permeability tight gas reservoirs are analyzed, and the chart between dimensionless pressure drop and recovery degree is established to evaluate the development effects of gas reservoirs in different periods. The simulation results show that the residual gas saturation determines the lag time of gas production. The lower the residual gas saturation is, the longer the flowback period of the gas well is. Through the research of this paper, the influence law of different reservoir physical properties on development effect is revealed, which has important theoretical and practical significance for guiding the efficient development of tight gas reservoir.

Research and Application of Multi-scale Support Mechanism in Tight Gas Reservoir

CHEN Chi, GUO Jianchun, LU Qianli, CI Jianfa

2022, 44(3):  131-138.  DOI: 10.11885/j.issn.1674-5086.2022.02.23.01

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Tight sandstone gas is an important unconventional natural gas resource, which requires fracturing to achieve effective development. In this paper, the tight sandstone outcrop cores in the Sichuan Basin are selected, and the rough fracture rock samples are carved to carry out multi-scale fracture conductivity and proppant backflow experiments, and analyze the influence of conductivity and proppant backflow. The results show that in order to obtain stable conductivity, the main fracture near the well needs to have enough proppant to provide a larger remaining fracture width, and only a small amount of small particle size proppant in the shear fracture of the far well can be effectively improved. For main fractures filled with proppant, the fracture conductivity has the critical closure stress and critical proppant concentration. Adding fibers to the proppant packing layer increases the sanding critical flow velocity by an order of magnitude, which can effectively prevent proppant backflow in fractures after fracturing. The multi-scale support concept of tight gas reservoirs has achieved significant stimulation effects in the fracturing engineering practice of tight gas reservoirs in the west Sichuan Depression of the Sichuan Basin, providing effective support and reference for the economical and efficient development of tight gas reservoirs.

Nano-plugging Low Damage Fracturing Fluid for Tight Sandstone Gas Reservoir

TAN Jia, LIU Yintao, PAN Baofeng

2022, 44(3):  139-147.  DOI: 10.11885/j.issn.1674-5086.2022.01.26.04

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To solve the problem that conventional guar gum fracturing fluid is harmful to tight sandstone gas reservoir, a kind of low damage nano-sealing fracturing fluid was developed by means of molecular structure design and orthogonal experiment. During the fracturing of tight gas reservoir, fracturing fluid can be blocked out of the reservoir matrix, and the liquid can be drained back quickly after the fracturing, so as to effectively reduce the retention and adsorption of thickener molecules and the damage of liquid phase. The fracturing fluid is sheared for 120 min at 35$\sim$140℃ and 170 s$^{-1}$, the final viscosity is over 80 mPa$\cdot$s, the gel can be broken thoroughly, the residue content is low, the surface tension of the GEL breaker is 25.91 mN/m, the damage rate to the tight sandstone core is less than 15%, and plugging performance and other comprehensive performance meet the requirements of field construction. Using this fracturing fluid in ZJ125 Well, the fluid performance is good, and the fluid flowing back is quick after the operation, the flowing back rate being as high as 75.94%, 47% higher than adjacent well; the natural gas output is 1.647 5 $\times$10$^4$ m$^3$/d, 2 times of adjacent Well JS316HF, showing that the gas reservoir has a good low retention property in tight sandstone gas reservoirs.

Volume Fracturing Application of Tight Sandstone in Zhongjiang Gas Field

LIN Yongmao, MIAO Weijie, LIU Lin, WANG Xingwen, QIU Ling

2022, 44(3):  148-156.  DOI: 10.11885/j.issn.1674-5086.2022.01.25.06

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The tight sandstone in Zhongjiang Gas Field in Western Sichuan has uneven distribution of channel sand bodies, large horizontal stress difference, low brittleness index, undeveloped natural fractures, and high extensional pressure gradient. The characteristics result in the low sand adding intensity of the transformation, high construction pressure, which makes the output after compaction is not ideal. This paper draws on the concept of "the shortest flow distance, the smallest flow resistance, and the largest control range", relying on the integration of geology and engineering, with multi-vector strong support volume stimulation as the key makes a study on the volume stimulation technology of tight sandstone in Western Sichuan. Based on the balanced expansion of fine seam technology, the segmented clustering of tight sandstone double sweet spots in Western Sichuan is optimized, and the lateral production rate is greatly increased. With two-stage composite support, high-displacement continuous sand adding and real-time control of variable viscosity liquid, the high sanding strength technology realizes multi-vector forced sand with multi-fracture coupled proppant combination. The double compound temporary plugging and forced diversion of multi-particle size temporary plugging balls between clusters and multiple combined temporary plugging agents in fractures improves the complexity of transverse fractures. The research results have been successfully applied and gradually promoted in the Zhongjiang Gas Field. The research results have increased the sanding intensity from 0.50 t/m to 4.18 t/m in the early stage, increased by 8 times. The average unblocked flow rate has been implemented at 557 000 cubic meters per day. EUR is 133 million cubic meters, and the transformation effect is significantly improved compared with the previous period.

Study on Damage Mechanism of Wellbore Fluid Accumulation Reservoir in Tight Sandstone Gas Reservoirs in Western Sichuan

LI Shengfu, LI Gao, WU Jianzhong, LI Ze

2022, 44(3):  157-166.  DOI: 10.11885/j.issn.1674-5086.2022.01.29.02

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The tight sandstone gas reservoir in western Sichuan is rich in reserves, but there is a phenomenon of wellbore effusion and serious reservoir damage, which affects the development efficiency. Understanding the damage mechanism of wellbore effusion reservoir is the premise and foundation to fundamentally solve the damage of effusion reservoir. In this paper, aiming at the damage problem of wellbore liquid accumulation reservoir in gas wells, quantitative evaluation experiments of wellbore liquid accumulation reservoir damage are carried out to analyze its damage mechanism. The results show that the reservoir water-sensitive minerals are easy to react with liquid; and small and medium pores, resulting in high capillary pressure, and in serious wellbore effusion damage. When the wellbore pressure increases 1 MPa, the reservoir damage increases about 6%. The damage degree of foaming agent to the reservoir increases with the increase of concentration, and the damage to the formation caused by foaming agent and condensate oil is greater. When the concentration of foaming agent is greater than 0.5%, the damage degree to the reservoir can reach more than 90%. The results provide a scientific basis for revealing the damage mechanism of wellbore effusion reservoir in tight sandstone gas reservoir in western Sichuan.

Method for Calculating Critical Liquid Carrying Flow Rate of Oil-gas-water Three-phase Horizontal Wells

WANG Xu, LU Guangliang, LUO Chengcheng, LIU Yonghui

2022, 44(3):  167-175.  DOI: 10.11885/j.issn.1674-5086.2022.01.26.03

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Horizontal wells located in medium-shallow layers of western Sichuan produce fluids to varying extents. When wells suffer from liquid loading, engineers must implement foam assisted lift or other technologies to stabilize the production. The easiest way to recognize liquid loading is to calculate the critical gas flow rate of gas wells. Two commonly used models for critical liquid carrying flow rate calculation are droplet and liquid film models, and the two models are established based on droplets or liquid film reversal as the onset of liquid loading. However, the result by the two models do not match well with observations in gas wells is low in the research area. To solve this problem, experimental investigation on liquid-loading behavior in horizontal gas wells and corresponding modeling study have been conducted. The results indicate that liquid is not yet loaded in wellbore when the droplets or liquid film are reversed. Therefore, predicted liquid-loading onset by the two models is too conservative. Then, a new criterion of liquid-loading onset is proposed based on the observed flow phenomenon and dragging capability of gas core. With the decrease of inclination, the measured critical gas flow rate increases first and subsequently decreases, reaching maximum at inclined angle of about 40°. Based on measured data and considering the effect of oil cut and inclined angle, a new liquid-loading predicting model was established. The new model was applied to prediction of liquid loading in wellbore of horizontal wells in the medium-shallow layers with oil-gas-water three-phase flow. The accuracy of the new model is 91.4%, suggesting that it is worth promoting and applying in similar gas wells.

Development and Application of New Foaming Agent for Gas Drainage in Middle and Shallow Layer of Western Sichuan

LI Zuyou, TANG Lei, YIN Hongyao, FENG Yujun

2022, 44(3):  176-187.  DOI: 10.11885/j.issn.1674-5086.2022.01.26.01

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The middle shallow gas well in the old part of Sichuan Basin has been in the low pressure and low production stage. The gas wells with wellhead pressure lower than 1 MPa accounted for 76.13%, and the production lower than 0.2$\times$10$^4$ m$^3$/d accounted for 57.14%; 80.62% of the gas wells have been involved in the bubble discharge process, but the effect of bubbling process is gradually getting worse. In view of the poor bubble drainage effect of high condensate oil and gas wells, the low bubble drainage efficiency of low-pressure and low production gas wells, and the difficulty of gas well treatment caused by the coexistence of effusion and emulsification, three new SCU series foam discharge agents have been developed. By establishing CHSB-SDS-PFBS ternary surfactant system, we developed a high anticoagulant oil bubble drainage agent SCU-2, which could reduce the gas-liquid surface tension to 26.73 mN/m and hold 50% content of anticoagulant condensate. Through the optimization of reaction system and catalyst, we developed self generated energy type foam discharge agent SCU-3, which could generate N$_2$ and heat in the wellbore and increase the foam lifting efficiency in low pressure and low production wells. Optimizing the combination of compound acid and oil resistant surfactant, we developed the purification and drainage integrated foaming agent SCU-6, which is better than conventional foaming agent for gas drainage in the properties of reducing viscosity and foaming ability with same concentration. Currently, SCU series foaming agent have been applied in 138 gas wells with 89.73% effective rate and 774$\times$10$^4$ m$^3$ gas production increase. The new foaming agent gas drainage expand the application scope of foam drainage technology and have excellent prospect of popularization and application.

Practice and Effect of Gas Production Technology in Western Sichuan Tight Sandstone Gas Field

DU Yang, GUO Xinjiang, LIU Tong, ZHANG Guodong

2022, 44(3):  188-196.  DOI: 10.11885/j.issn.1674-5086.2022.02.28.01

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The Jurassic gas reservoir in western Sichuan is a typical low-porosity and low-permeability sandstone gas reservoir, which produces a small amount of formation water during the development of the gas reservoir, and there is no obvious edge and bottom water or inter-layer water. With the continuous development of the gas field, the accumulation of fluid at the bottom of gas wells has intensified, resulting in rapidly decline of production and pressure, short stable production period and long low-pressure and low-production production time, and deliquification technology is a key factor for long-term stable gas production. Based on 25 years of research and practice, a set of diversified wellbore diagnostic techniques for water-producing gas wells is established and improved, based on flow-pressure measurements, echometer test and empirical methods, according to the law of gas well energy change, a differentiated foam drainage technology, supplemented by complementary gas lift deliquification and velocity strings artificial lift methods is formed, by the development of digital technology, a management system of "fine diagnosis + intelligent process integration" is proposed, intelligent supporting devices such as online diagnosis of fluid accumulation, cluster wells foaming and plunger lift device is developed. Through more than 1 200 gas wells application, it has effectively improved the effect of gas well drainage and production stabilization, and reduced the reduction of comprehensive decline of old wells, which has certain significance for the development of similar gas fields at home and abroad.

Research on the Retrograde Condensate Damage and Development Strategies in Tight Sandstone Gas Reservoir

LI Feng, ZHANG Benyan, ZHU Jing

2022, 44(3):  197-206.  DOI: 10.11885/j.issn.1674-5086.2022.01.24.05

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Retrograde condensation damage of gas reservoirs decreases the productivity of the gas well during the development of Shaximiao Formation in Zhongjiang Gas Field. According to the characteristics of fluid phase change in gas reservoir, the influence of retrograde condensate on gas reservoir development is evaluated by retrograde condensate damage experiments for the long core and numerical simulation analysis. The results show that during the development of the gas reservoir, the retrograde condensate damage will greatly reduce the gas phase permeability. The core permeability damage rate is 32%, and the maximum condensate saturation is 1.8%. The fracturing can effectively reduce the degree of the retrograde condensation damage, the higher the reservoir permeability is, the smaller the effect of reverse condensation on gas well productivity is. Based on the analysis of the production characteristics of Shaximiao Formation in Zhongjiang gas field, it is suggested to prolong the producing time above the dew point pressure by reasonable production allocation of gas wells in the early stage of production, means of foam drainage and plunger gas lift in the later stage can be used to discharge the accumulated oil in the wellbore, to ensure the stability of gas wells and ultimately improve the development benefit of gas reservoirs.

A Study on Compound Pollution Control Technology Immediate Vicinity of Wellbore of Tight Gas Reservoir in Western Sichuan

LEI Wei, XU Jian, ZHAO Zhejun, LIU Tong

2022, 44(3):  207-214.  DOI: 10.11885/j.issn.1674-5086.2022.01.28.01

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Aiming at the problem of reservoir pollution in the near well zone of tight gas reservoir in Western Sichuan, the characteristics and components of pollutants are analyzed, and the main pollution types in the near well zone of tight sandstone gas reservoir in Western Sichuan are defined. Secondly, a multi-functional composite plugging removal agent was developed, and the evaluation tests of the physical properties, scale dissolution ability, demulsification and viscosity reduction, core displacement and so on of the new agent were carried out. Thirdly, the near well zone pollution model of fractured wells is established, and the deep purification process of "large liquid injection, strong liquid nitrogen displacement and blowout assistance" is put forward. Finally, it is popularized in Luokou Gas Field and Zhongjiang Gas Field. The results show that the efficiency of the new process measures is 90% and the natural gas production is increased by 1 923$\times$10$^4$ m$^3$, which has achieved obvious economic benefits. The conclusions are as follows:(1) the near well zone pollution of tight sandstone gas reservoir in Western Sichuan is the compound damage of liquid locking, foaming agent emulsification, fracturing fluid damage and scaling crystallization; (2) the multi-functional composite plugging remover has many functions, such as dissolving inorganic scale, breaking emulsion and reducing viscosity, and removing water lock. After displacing the polluted core, the permeability can be increased by 1.74$\sim$2.4 times; (3) the deep purification process of "large liquid injection, strong displacement of liquid nitrogen and blowout assistance" can improve the penetration depth of purification agent in tight reservoir and improve the pollutant flowback efficiency. It has popularization value in similar gas reservoirs.

Key Technologies and Applications of High-efficiency Surface Gathering and Transportation in Zhongjiang Gas Field

FU Xianhui, YAO Linyu, WANG Quan, LUO Linjie, WANG Xiaogang

2022, 44(3):  215-223.  DOI: 10.11885/j.issn.1674-5086.2022.01.28.02

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Aiming at the problems of rolling development of ZJ Gas Field, high pipeline network pressure caused by rapid production ramp-up, difficulty in production of low-pressure and low-yield wells, and interference between wells at the same well site restricting the production release of low-pressure wells, three surface high-efficiency measures for pipeline network, station site and gas well, research and application of key technologies for gathering and transportation were carried out. Firstly, multi-scheme structural optimization simulation was carried out based on the existing pipeline network, and a figure-8 "branch + ring" composite pipeline network was established, which doubled the gathering and transportation capacity and reduced the back pressure at the far end of the gas field by 0.5 MPa, ensuring natural gas second, for axially distributed low-pressure and low-yield gas wells, a systematic evaluation of the technical and economic limits of 5$\sim$10 km multi-node booster radius was carried out, and a 10 km long-radius booster scheme for the ZJ Gas Field was formed, which increased the coverage by 30% and reduced the construction cost by 25%, to realize low-cost pressurization of gas wells distributed in narrow and long strips; finally, for the high and low pressure gas wells in the same well site, a "movable + low pressure difference" ejector device was developed, which reduced the conventional ejection pressure difference from 3.0$\sim$5.0 MPa to 0.4$\sim$1.0 MPa, realizing the injection booster of the low-pressure well relative to the high-pressure well in the same well station without the external power source. The high-pressure gas well at the well site inhibits the production of the low-pressure gas well; the key technologies of efficient surface gathering and transportation in the ZJ Gas Field effectively support the smooth realization of the gas field production target and ensure the "production and output".

Development and Application of Non-limited Sliding Sleeve with Switch Function

HU Dan, HU Shunqu, CHEN Chen, HOU Zhimin, ZHOU Yijun

2022, 44(3):  224-234.  DOI: 10.11885/j.issn.1674-5086.2022.02.07.02

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Tight sandstone gas reservoirs is characterized by tightly rocks and low natural productivity. Infinite staged fracturing technology for horizontal wells is the necessary means of high efficient development for this gas reservoirs. It is difficult to implement measures such as reservoir evaluation and wellbore maintenance due to the limited segmented stages of ball throwing sliding sleeve and pipe string shrinkage, although the plug and perfortion can achieve infinite stages, but the construction is not continuous, operating costs are high. Meanwhile, those fracturing tools have single function, which cannot meet the needs of water control of production wells. According to the function requirement of "non-limited, full-bore, switchable, combined operation" gas reservoir, the theory of full-bore non-limited design is innovated, the open assembly with compound shrapnel-multi-function ball cage structure and the sliding sleeve body with position selection slot and inner rubber cylinder are designed, and the full-diameter sliding sleeve structure with infinite stage is formed. The tool system has been used to nearly 200 wells in tight sandstone gas reservoirs in Western Sichuan Basin. Compared with the same technology at home and abroad, the operating efficiency can be improved by 50%, the selective switch operation is successfully carried out in production wells such as DS103-2. It provides a new tool system for efficient development of tight sandstone gas reservoirs.