Sulige Gas Field Research Articles

Sedimentary facies and diagenesis control on petrophysical properties of sandstone reservoirs: A case study from the Permian Sulige Gas Field, Ordos Basin (Central China)

The sedimentary characteristics and petrophysical properties of the reservoir of the second/lower member of the Lower Permian Shanxi Formation (P1s2) in Sulige Gas Field, Central China are studied by means of thin section petrography and scanning electron microscopy. This article highlights the relationship between reservoir quality and sedimentary environments, explains the differences in reservoir petrophysical properties in different sedimentary environments, discusses the influence of clastic components and authigenic minerals on the reservoir, and finally, provides the basis for the prediction of relatively high‐quality reservoir in P1s2 of the study area. The results show that the sandstones formed as a meandering river deposit in the south of the study area are fine‐grained, mainly composed of lithic fragments of quartz sandstone, metamorphic, and volcanic rock lithic fragment, with high content of matrix and poor sorting, average porosity of 5.09%, and average permeability of 0.20 × 10−3 μm2. The braided river sedimentary deposits in the north are coarse‐grained, mainly composed of quartz sandstone sedimentary rock lithic fragment, with low content of matrix, good sorting, and more developed dissolution pores. The average porosity is 6.16%, and the average permeability is 0.53 × 10−3 μm2. Among the authigenic minerals, siderite, calcite, and illite block, the pores between the grains reduce the porosity. Siliceous cement often indicates better reservoir petrophysical properties. The siliceous cement is more common in braided river deposits in the north area, in which the channel bar detailed facies are conducive to retain more primary pores or form secondary pores, thus forming better reservoirs.

Reservoir Characteristics and Its Comprehensive Evaluation of Gray Relational Analysis on the Western Sulige Gas Field, Ordos Basin, China

Although the Sulige gas field has been developed for several years, accurate reservoir classification, evaluation, and prediction is still a worth-exploring scientific issue as this is a necessary procedure which could give the guidance of well deployment during later gas field development. Here, based on the analysis of lithological features and diagenesis, we give an evaluation of gas reservoirs in the western Sulige gas field by using the improved method of gray relational analysis. Our results show that the study area Su-54 block is dominated by low permeability and low porosity litharenite and lithic silicarenite with clear evidence of strong diagenesis processes. Compaction is believed to be relatively strong due to the great burial depth and destroy most of the primary pores. Based on the premise of a lower limit of an effective reservoir, we select five parameters (permeability ( K ), porosity ( Φ ), effective sand thickness ( M ), effective sand/sand thickness ratio ( D ), and gas saturation ( S g )) to calculate the correlation coefficient, relational degree, and index weights for reservoir quality evaluation. By weighted gray correlation theory, the dynamic testing data—effective thickness of gas production data—is used as mother sequences. The results show that the predicted favorable areas for gas exploration and development coincide well with sedimentary and sand body distribution (e.g., point bars and central bars) in the study block; well blocks such as s372, s373, s374, and e24 could be future key development targets. This also indicates a broader application of the gray relational analysis to quality evaluation and distribution prediction of reservoirs. Therefore, our findings could give a new theoretical and practical guidance for the later gas exploration and development, for the search of hidden stratigraphic lithological traps, and for the improvement of the proven rate of oil and gas resources in this area.

Single well control area splitting method based on reservoir sphysical properties and gas well productivity differences

The determination of the control area of a single well is the prerequisite for the evaluation of the reserves of a single well. The current calculation methods of the control area of a single well are mainly divided into: experience formula, area balancing method, and the physical model, in order to solve the different limitations of the existing single-well control area splitting method and the problem of large error in use, this paper puts forward a kind of based on gas reservoir physical property and the growth of single well productivity difference algorithm for single well control area is split, according to the results of the split combining static reservoir parameters, using volumetric method for single well and the calculation of reserves of gas reservoir evaluation, further clarify the original and the remaining gas distribution of gas reservoir, for the subsequent reasonable development of the gas reservoir and enhance oil recovery. In this paper, block S of Sulige gas field is taken as an example, and the geological reserve of block is calculated as 354.75×108m3, compared with the basic proven reserves of Block S, 364.84×108m3, the error is 2.61% and the reliability is strong

Formation and diagenetic characteristics of tight sandstones in closed to semi-closed systems: Typical example from the Permian Sulige gas field

In a closed to semi-closed diagenetic environment, the migration efficiency of diagenetic fluid is low, material exchange is weak, and the diagenetic processes of dissolution and cementation differ greatly from those in an open diagenetic environment. Previous research on closed to semi-closed diagenetic systems has focused on the formation mechanism of tight sandstones and the factors that control the formation of high-quality reservoirs. In this study, we obtained data from measured physical properties, petrographic microscope images, scanning electron microscope images, nuclear magnetic resonance, and electronic CT scans from the Permian Sulige gas field, located in the Ordos Basin, North China. We comprehensively analyzed the diagenetic characteristics, diagenetic evolution, compaction mechanism of tight sandstones in closed and semi-closed diagenetic environments, as well as the relationship between compaction and accumulation within this environment. The findings showed that sandstone densification in this area is characterized by multiple stages of siliceous and calcareous cementation. The diagenetic evolution of the Sulige field suggests that the sandstone densification process was not the result of conventional compaction/reduction of porosity and simple cementation, but rather was caused by compaction and quasi-continuous solution-cementation. The migration of organic acids in this process was instrumental for dissolution and pore development, and induced the densification of sandstone. During the dissolution process within the reservoir, the dissolving fluid was retained insitu, thus forming different cements that corresponded to particular periods. We propose that the quasi-continuous dissolution and cementation that occurred during diagenesis was the main cause of densification in the sandstone reservoirs of the Sulige field closed to semi-closed systems. The findings of our study provide a new direction for ongoing research in the field of development of high-quality reservoirs.

Insight into the Pore Structures and Its Impacts on Movable Fluid in Tight Sandstones

Both the characteristics of pore structure and movable fluid are significant properties in controlling the flow regularity in pores in tight sandstones. However, the governing factors that affect the fluid flow features will still be a myth. In our research, the western area of the Sulige gas field was chosen as the research region, and various kinds of experiments were conducted. Three reservoir groups, including intergranular-dissolved pore type, dissolved-intercrystalline pore type, and pore plus microcracks type were identified on the basis of pore development features. The results suggest that the intergranular-dissolved pore type has a more prominent influence on the high movable fluid saturation and larger pores. Both large throat sizes and homogeneous pore-throat degree demonstrate high movable fluid saturation. The increment of the thickness of water-film resulted from hydrophilic enhancement, indicating that an increased hydrophilic will decrease the movable fluid saturation and block the throats. The reservoirs of different pore combination types are closely related to the gas content of the reservoir.

Eogenetic karst and its control on reservoirs in the Ordovician Majiagou Formation, eastern Sulige gas field, Ordos Basin, NW China

Abstract To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin, the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken as examples to analyze the vertical development characteristics of eogenetic karst and to discover the dissolution mechanism and its control on reservoirs through observation of a large number of cores and thin sections. According to detailed analysis of petrologic characteristics, the reservoir rock types include micritic dolomite, grain dolomite and microbialite which have mainly moldic pore, intergranular (dissolved) pore, and (dissolved) residual framework pore as main reservoir space respectively. The study area developed upward-shallowing sequences, with an exposure surface at the top of a single upward-shallowing sequence. The karst systems under the exposure surface had typical exposure characteristics of early dissolution and filling, indicating these reservoirs were related to the facies-controlled eogenetic karstification. With the increase of karstification intensity, the reservoirs became worse in physical properties.

Production Performance Analysis of Su-6 Well Block in Sulige Gas Field, Ordos Basin, China

As a tight sandstone gas reservoir of Su-6 well block in Sulige gas field, part of the gas wells have a poorer production performance with a faster decline rate of formation pressure and production, which is inconsistent with static reservoir parameters of gas well. In order to improve the productivity of gas well, on the base of static and dynamic classification of 232 gas wells, the reasons of inconformity between production performance and static reservoir parameters are analyzed from the four aspects of sand body connectivity, reservoir heterogeneity, gas saturation and fluid accumulation in wellbore. The results show that the main reasons causing the inconformity are the strong heterogeneity and poor sand body connectivity, and the secondary reasons are fluid accumulation in wellbore and low gas saturation. The results of this paper is of great significance to improve the productivity of gas wells and guide the development of ultra-low permeability gas reservoir.

Diagenetic alteration, pore-throat network, and reservoir quality of tight gas sandstone reservoirs: A case study of the upper Paleozoic sequence in the northern Tianhuan depression in the Ordos Basin, China

The Sulige gas field in the Ordos Basin is the largest gas field in China. The studied area, the northern Tianhuan depression, is located west of the gas field and is considered as a potential gas-producing area. The complex diagenetic alteration history and its effects on the pore-throat network and reservoir quality of the tight gas sandstones are explained. The upper Paleozoic first member of the Shanxi Formation and eighth member of the Shihezi Formation tight gas reservoir rocks are composed of coarse- to medium-grained sandstones and are dominated by sublitharenites. The most important diagenetic factor for porosity reduction was compaction, followed by cementation. Diagenetic mineral phases include quartz overgrowth, calcite cement and replacement, and kaolinite cement and replacement, with minor heulandite and chlorite. Pressure dissolution of quartz grains and quartzite fragments is the main source of silica for the early and late quartz overgrowth cementation (formed mainly from 120°C to 140°C). The hydrolysis and alteration of volcanic material and mica flakes released some silicon, calcium, and aluminum ions. Calcium and carbon in calcite cements could be derived from surrounding mudstones. Calcite replaced the quartz overgrowths. The formation of kaolinite, as cement and replacements, was controlled by the interactions of silica, aluminum, pH, and temperature (140°C). Because of deformation of detrital components (mica flakes and ductile rock fragments) and diagenetic replacement, clear negative correlations between reservoir quality and contents of the diagenetic minerals are lacking. A complex and isolated pore-throat network was created by strong diagenetic transformation. Based on analysis of thin sections, three-dimensional x-ray micro–computed tomography, and constant-rate mercury injection data, the samples with relatively good reservoir quality (porosity >10% and permeability >0.5 md) are characterized by dissolution pores and primary intergranular pores and commonly contain more and larger pore throats both in volume (counts >1800 and size >0.02 per unit volume) and diameter (>1.20 μm) than the samples with poor reservoir quality. The intercrystalline pores of kaolinite are very widespread and considered favorable for oil and gas accumulation because some asphalt was found within these pores. This study may be used, by analogy, to better understand diagenetic factors controlling the formation of tight gas sandstone reservoirs and predict the development of pore-throat systems.

Engineering-oriented “sweet spot” prediction for tight sandstone gas reservoirs: A case study from Sulige gas field in Western China

Tight sandstone gas reservoirs have the characteristics of low porosity and permeability, deep burial, and low production of vertical wells, which are difficult to predict and exploit. Usually, finding a “sweet spot” requires finding zones with well-developed fractures or easy stimulation by hydraulic fracturing in the later stage. For some tight sandstone gas reservoirs where natural fractures are not developed, directional hydraulic fracturing is a good choice to improve single well production. However, not all reservoirs can achieve the desired productivity after hydraulic-fracture stimulation. In the exploration of the Sulige (SLG) gas field in Western China, sweet spots with strong brittleness and good petrophysical properties can ensure the success of hydraulic fracturing. We have evaluated the SLG gas field to determine how to implement an engineering-oriented sweet spot prediction workflow. The method has five steps: data-quality analysis, lithology prediction, brittleness prediction, petrophysical property prediction, and well planning. We evaluated the feasibility of subsequent sensitive elastic parameter inversion by comparing the accrual and simulated seismic gathers. Then, we used a direct inversion method of Young’s modulus to predict lithology and identify fluid at the same time. Next, we constructed a new brittleness index by combining the rate of change of Young’s modulus and the quartz content to evaluate the brittleness of rocks, which can overcome the shortage of the conventional brittleness index constructed by a single parameter. Finally, by using the brittleness index, we combined the petrophysical properties inversion results to select regions with strong brittleness and good petrophysical properties as the basis of well planning. This workflow achieved remarkable results in the exploration of tight sandstone gas reservoirs in the SLG gas field in Western China.

Study of the Effect of Movable Water Saturation on Gas Production in Tight Sandstone Gas Reservoirs

The movable water saturation of tight sandstone reservoirs is an important parameter in characterizing water production capacity, and there is a great need to understand the relationship between movable water saturation and water production characteristics. However, movable water behavior in this context remains unclear. In this study, four groups of tight sandstone cores from the Sulige gas field are measured to understand the movable water saturation characteristics. Then, the effects such as reservoir micropore throat, clay mineral and physical properties on movable water saturation are analyzed, and the movable water saturation and water production characteristics are discussed. The results show that higher movable water saturation will result in a greater amount of water in the gas drive. There is a critical pressure difference of the gas drive, and a large amount of movable water will flow out. Movable water saturation is independent of the porosity, permeability and initial water saturation, while it is closely related to the reservoir micropore throat and clay mineral content. Movable water is mainly distributed in the medium and large pores; the larger the proportion of such pores, the higher the degree of movable water saturation. A lower mineral content will lead to higher movable water saturation in tight sandstone gas reservoirs. These results provide clues for identifying gas–water bearing reservoirs and evaluating and predicting the water production characteristics in gas wells in tight sandstone gas reservoirs.

Genesis of dolomite in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, China: Evidence from C, O, and Sr isotopes and major and trace elements

Typical dolomite reservoirs exist in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, however, the current understanding of dolomite genesis needs to be clarified. This study confirms the dolomitization characteristics, diagenetic environment, and genesis of dolomite through the use of core observations, thin section identification, and geochemical data (carbon and oxygen stable isotopes, strontium isotopes, and major and trace element contents). The results showed that dolomite samples from the study area includes micritic dolomite, powder crystal dolomite, and micrite to powder crystal dolomite, in which the main reservoir space consisted of intergranular pores, intercrystalline pores and various dissolved pores. The δ13C value of the dolomite samples ranged from −7.26‰ to1.28‰ with an average of −0.45‰, which is equivalent to that of seawater during the Ordovician. The δ18O value ranged from −9.94‰ to −6.32‰ with an average of −7.86‰, which is clearly more negative than that of the Ordovician seawater. The 87Sr/86Sr ratio varied from 0.70867 to 0.71033 with an average of 0.70946, which is significantly more positive than that of Ordovician seawater. The Mg/Ca ratio was lower than that of the seawater and close to 1:1. Overall, all of the samples were characterized by high Fe and Mn contents, while low Sr and Na contents. These results clearly indicate that the dolomitized fluid was closely related to seawater or a sea-source fluid. Furthermore, the restored paleosalinity, paleotemperature, and paleodepth also indicate that the dolomite was formed in a marine reducing environment. Combined with the petrological characteristics and geochemical indicators, two dolomitization models (mixed water dolomitization and burial dolomitization) were established for the upper assemblage of the Ordovician Majiagou Formation in southeastern Sulige gas field. We infer that mixed water dolomitization was dominant before the Carboniferous, whereas burial dolomitization was dominant after the Early Permian.

Geophysical Research Progress On Tight Sandstone Reservoir In Sulige Gas Field

Geophysical Research Progress On Tight Sandstone Reservoir In Sulige Gas Field

Evaluation and application of poly(ethylene glycol) as lubricant in water‐based drilling fluid for horizontal well in Sulige Gas Field

AbstractWith the increasing amount of drilling of directional wells and large‐displacement wells, high torque and high resistance have become critical problems. Therefore, high‐performance and environment‐friendly lubricants for water‐based drilling fluid are urgently needed. In this paper, poly(ethylene glycol) 2000 (PEG) was used as a lubricant, and the lubricity, inhibition, compatibility and temperature resistance of the PEG lubricant were investigated. The results show that 0.1% (mass ratio) PEG in water‐based drilling fluid can reduce the friction coefficient of mud cake by 44.5%. This PEG also has certain inhibition and temperature resistance. As PEG is used with other drilling fluid additives, the compatibility was good and the lubricity of drilling fluid can be improved effectively. The lubricating mechanism of PEG was explored and the results showed that the hydrophobic alkane chains in the PEG molecules were adsorbed on the surface of bentonite, forming a hydrophobic film on the friction surface, thereby forming a lubricating layer. Field application in Sulige Gas Field showed that the PEG lubricant has good lubricity and can meet the technical requirements of corresponding horizontal wells. © 2020 Society of Industrial Chemistry

Well network optimization and recovery evaluation of tight sandstone gas reservoirs

Tight sandstone gas reservoirs differ greatly in physical properties, and this kind of uncertainties severely set a limit to the steady production and efficient development of gas reservoirs. In order to effectively develop untapped reserves of tight sandstone gas reservoirs and improve their production and recovery, it is important to optimize the well pattern density for the ones with complex reservoir conditions. In this paper, a new index parameter is proposed for the optimization of well pattern density and recovery of tight sandstone gas reservoirs with complex reservoir conditions: the dynamic single-well control area (DSWCA). And the fuzzy synthetic evaluation method is used to establish the relationship between DSWCA and 7 reservoir physical parameters when there is no inter-well interference. The seven parameters are permeability, porosity, effective thickness, water saturation, threshold pressure gradient, productivity coefficient and storage coefficient. Besides, the calculated fuzzy prediction value of the DSWCA is compared with the geological well control area to determine whether there will be inter-well interference due to well pattern infilling under different physical reservoir conditions, and the variation curve of the interference probability with well pattern density is obtained. Finally, a gas recovery evaluation model is constructed combined with inter-well interference probability. The new evaluation method and model derivation comprehensively evaluate the influence of multiple reservoir physical parameters on the DSWCA and the quantitative relationship among them, thus capable of effectively calculating the DSWCA and predicting the production and recovery of the gas field beforehand from a very early stage using the related parameters. The new method, combined with a large number of physical parameter data of fractured vertical wells, was applied in the Su-6 block of the Sulige gas field and compared with the results of actual gas well production dynamics, revealing the consistency of the two results. This method is verified to be reasonable and reliable under certain conditions, and the new method for gas recovery evaluation provides new ideas for the well pattern optimization in tight sandstone gas reservoirs.

A method to remove depositional background data based on the Modified Kernel Hebbian Algorithm

The seismic sedimentology is an emerging inter-discipline originating from the seismic stratigraphy and sequence stratigraphy. However, implementation of the seismic sedimentological research is found with high difficulties, due to influences imposed by structural and depositional background data (including strong reflections). In this paper, seismic records are regarded as a combination of the reflection from the depositional background and lithological data volumes, and moreover, the seismogram of the depositional background data is characterized by the low frequency and stable phase. Subsequently, the Kernel Hebbian Algorithm (KHA) has been modified to remove the influence of the depositional background data. The seismic trace data are used as the training set, and an innovative attempt has been made to incorporate the Ricker wavelet kernel function. Finally, a depositional background data volume extraction methodology with respect to input of higher-dimension seismic data has been developed, on the basis of the Modified KHA (MKHA), so as to obtain the lithological data volume. Utilizing the unsupervised online learning capabilities of the MKHA, iterative calculation of Kernel PCA can greatly reduce the computational complexity and can be adapted to big data problems. This paper introduces the Ricker wavelet kernel function to transform the original seismic data into the feature space through the inner-product operation, extract the non-linear features, and solve the problem that the seismic data of the original sample space is linearly inseparable. The seismic sedimentological analysis based on the lithological data volume that is able to reflect hidden sand bodies can achieve elaborate carving of the reservoir. The proposed method has been tested in Working Block A of the East-1 district in the Sulige gas field, the Ordos Basin, China. The case study demonstrates that the presented method is capable of efficiently removing the depositional background data, and making great contributions to improving accuracy of the seismic sedimentological analysis of the effective reservoir, with the help of higher-dimension seismic data.

Effects of pore structures on the movable fluid saturation in tight sandstones: A He8 formation example in Sulige Gasfield, Ordos Basin, China

A complex pore structure is a crucial factor influencing the movable fluid saturation in tight sandstones, which poses a significant challenge to the exploration and development of the He8 formation in the Sulige Gasfield. To confront this challenge, various experimental methods, including, thin section, scanning electron microscopy (SEM), cathode luminescence (CL), high pressure mercury injection (HPMI), constant rate mercury injection and nuclear magnetic resonance (NMR), were introduced to investigate the factors that affect the movable fluid saturation. The results showed that coarse to medium-grained quartz sandstone and lithic quartz sandstone were the dominant sandstone types. The main pore types were intercrystalline pores and dissolution pores. The mercury injection and NMR test results showed that the pore structure can be divided into three main types with different curve morphologies and different peak amplitudes. The pore structures were highly correlated with movable fluid saturation. Multiple factors were shown to influence the movable fluid saturation, including pore radius, throat radius, pore-throat radius ratio, sorting coefficient, pore mercury saturation and throat mercury saturation. Among these factors, throat radius and pore mercury saturation were dominant in influencing the movable fluid saturation in all three types. The throat mercury saturation had the greatest effect on type 3, demonstrating that the throat volume strongly contributed to the total volume in tight sandstones. The pore-throat radius ratio, and the sorting coefficient, had a degree of influence on the movable fluid saturation. Meanwhile, strong diagenesis was the internal reason for the complex pore structure that further influenced the movable fluid saturation. Mechanical compaction and cementation led to the rearrangement and compactness of detrital grains, which resulted in the reduction of effective space and the decline in the movable fluid saturation. Feldspar dissolution and debris dissolution provided significant storage space and enhanced the seepage capacity.

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10−3 µ m2, gas saturation could be greater than 50%.

Improvement of petrophysical workflow for shear wave velocity prediction based on machine learning methods for complex carbonate reservoirs

Shear wave velocity (S-wave velocity or Vs) is one of the most critical issues for carbonate reservoirs characterization, because of its complexity of rock compositions and pore structures. The Xu-Payne petrophysical model is a commonly used method to predict S-wave velocity. However, the model excessively depends on the interpretation accuracy of rock compositions, pore structures, fluid properties and fluid saturation, which makes the prediction result potentially uncertain. With the development of intelligent algorithms, a machine learning method (Long-short Term Memory Neural Network, LSTM) is proposed to improve the traditional petrophysical workflow. With the capabilities of deep learning and data mining, the LSTM model can deeply mine the rich information in the wireline logs and then establish the relationships between S-wave velocity and wireline logs. In order to illustrate the prediction effect, the carbonate reservoir in the Majiagou Formation Member 5(Ma 5 Member) which belongs to the Ordovician system in the D area of Sulige gas field is taken as an example. Six kinds of sensitive wireline logs, including compensated acoustic log (AC), natural gamma ray log(GR), photoelectric absorption cross-section log (PE), density log (DEN), deep lateral resistivity log(RLLD), neutron log(CNL), are selected as the input data of the LSTM model. The results reveal that the accuracy of LSTM method is up to 98.9%, whereas the Xu-Payne model is only 73%. With the predicted result of all wells in the areas using LSTM, the sensitive elastic properties, including P-and S-wave velocity, P- and S-wave impendences, ratio of P- and S-wave velocity, Poisson's ratio, lame coefficient and fluid sensitivity factor, are also concluded. Compared with the Xu-Payne model, the newly proposed workflow is proved to be convenient and suitable for the prediction of S-wave velocity in carbonate reservoirs.

A new method for well pattern density optimization and recovery efficiency evaluation of tight sandstone gas reservoirs

For the sake of improving the reliability of the method for well pattern density optimization of tight sandstone gas reservoir and effectively demonstrate the relationship between well pattern density and recovery efficiency, the well interference probability curve of the target study area in the Sulige Gas Field was plotted by establishing the calculation method for well interference probability. Then, a new method suitable for well pattern density optimization and recovery efficiency evaluation of tight sandstone gas reservoirs was established. Finally, this new method was applied in three encryption test areas of the Sulige Gas Field. And the following research results were obtained. First, the well interference probability of tight sandstone gas reservoir is heavily dependent on the well pattern density. With the increase of the well pattern density, the well interference probability presents a gradual increasing trend. And the well interference probability doesn't reach or approach to 1 until the well pattern density reaches a higher value. Second, in the three encryption test areas of the Sulige Gas Field, the economically optimal well pattern density is in the range of 2.6–3.1 wells/km2, and its corresponding recovery efficiency is 36.6–39.8% and corresponding well interference probability is 28–33%, while the economic limit well pattern density is in the range of 5.2–6.6 wells/km2, and its corresponding recovery efficiency is 46.8–49.8% and corresponding well interference probability is 83–89%. Third, the well interference probability corresponding to the economically optimal well pattern density of tight sandstone gas reservoir in the Sulige Gas Field is about 30%, and that corresponding to the economic limit well pattern density is about 85%. In conclusion, by virtue of this new method, the economically optimal well pattern density and the economic limit well pattern density and their corresponding recovery efficiencies can be calculated, so as to realize the well pattern optimization and recovery efficiency evaluation of tight sandstone gas reservoirs. The research results can provide theoretical support for the economic and efficient development of the Sulige Gas Field, and useful reference for the benefit development of the same type of gas reservoirs.

Economic Applicability Evaluation of Drainage Gas Production Technology in Tight Sandstone Gas Reservoir

With the development of Sulige gas field, the recovery degree of the gas field increases gradually, the formation energy decreases continuously, the proportion of water-producing gas wells increases year by year, and drainage gas production has gradually become the main technical means to stabilize production and increase production. Under the requirement of low cost, quality improvement, efficiency enhancement and benefit development, according to the production characteristics of gas wells in Sulige gas field, a judgment model of gas well liquid accumulation is established. Sensitivity analysis and model simplification of critical liquid carrying flow method are carried out to analyze the economic applicability of various drainage gas production technologies. The research shows that the early intervention of drainage gas production technology in gas wells at the initial stage of liquid accumulation can effectively prolong the period. Gas well life cycle, improve gas well recovery.