Advanced Materials Research Vol. 868

Abstract: Via discussing the advantages and disadvantages of different types of oil-based drilling fluids, the main reason why oil-based drilling fluids are less used in our country is obtained that dont form a complete series of matching technology. The essence of wellbore instability caused by using water-based drilling fluids to drill shale is analyzed that the formation collapse pressure is greater than drilling fluids column pressure. The fundamental way of controlling borehole wall stability that use water-based drilling fluids to drill shale horizontal well was proposed that deeply researched the shale hydration mechanism, developed efficient blocking agent and inhibitors and established shale gas drilling fluid suppression system, which made water-based drilling fluids have excellent performance.

Abstract: Banded gas reservoir with bottom water is a typical gas reservoir. Based on the development characteristics of formation, the further study on commingling production by transverse horizontal well is done, and also combined with seepage theory including the Green function, Duhamel method etc. the dimensionless definitions of relative parameter are given. Whats more, the derivation and formula of production can be achieved respectively under the constant pressure condition and constant production condition. Meanwhile, take commingling production with three banded gas layers for example. Whether the initial pseudo pressure for these layers are equal or not, in both of these cases, the variation curve of gas productivity under the constant pressure and constant rate conditions is described separately. And the law of variation of gas flow backward for some layer when the physical properties of these layers are significantly different.

Abstract: Surfactant imbibition experiments were carried out with four surfactants and effects of interfacial tension and surface wettability on oil recovery were studied. A convenient imbibition process with quartz sands was used, and the experimental results suggest that anionic and non-ionic surfactants have higher oil recovery than cationic surfactant, and the sand surface wettability plays an important role in influencing oil recovery during spontaneous imbibition. Altering the wettability of oil sand surface from oil-wet to water-wet can enhance the oil recovery of imbibition process. The maximum ultimate imbibition recovery appeared in the area where both contact angle and interfacial tension were low.

Abstract: Based on the coal reservoirs geological feature and coalbed methane (CBM) wells production data, and taken FS-2 well in the southern Junggar Basin as examples, history matching and productivity prediction of FS-2 well were conducted by using COMET3 numerical modeling software and the influence factors sensitivity of gas well productivity in the study area were analyzed. The results suggest: FS-2 well total gas production in the eight years was 2915007 m³, and the average daily gas production reached 1209.5m³/d, the CBM well belongs to medium production well. Permeability and gas content has the most effect on the single wells production in the study area, so the influence of the fracture half-length and coal seam thickness is weakened.

Abstract: In recent years, the research on the coal-bed methane productivity evaluation with the logging method has progressed slowly, and a great breakthrough is needed. The influencing factors of the coal-bed methane productivity are analyzed based on the characteristics of coal-bed methane reservoir and the principle of coal-bed methane exploration. And the methods of evaluating the logging reservoir parameters related to the coal-bed methane productivity are also discussed. Meanwhile, the research prospect on the evaluation of coal-bed methane productivity with the logging technology is proposed by utilizing the principle of complex oil-gas reservoir productivity evaluation.

Abstract: CO₂ flooding can increase coal bed methane production rate, enhance coal bed methane recovery and store CO₂ into underground. It has good application prospect for CBM development. This paper analyzes the adsorption-desorption law of mixed gas in the coal during the CO₂ injection process, as well as the diffusion and seepage law of gas in the coal seam. The sensitivity of factors affecting coal bed methane production is studied and then the coal bed methane production under different conditions is simulated numerically. The results show that methane concentration and coals permeability are the two key factors affecting the output of coal bed gas and their influence on productivity are even more significant than injection pressure and initial pressure. The higher injection pressure, coals permeability and gas concentration, the greater amount of methane the coal reservoirs will yield. When the coals permeability and the gas concentration in coal reservoirs increase, the growth rate of methane production accelerates accordingly.

Abstract: In acid fracturing, excessive acid leakoff is thought to be the main reason that limits fracture propagation and live acid penetration distance, so its very important to do research about acid leak-off on naturally fractured carbonates. we developed a new model in this paper to simulate acid leakoff into a naturally fractured carbonates gas reservoir during acid fracturing. Our model incorporates the acid-rock reaction on the fractured surfaces. Given the information of the Puguang gas reservoir, the model predicts acid filtration and leakoff rate over time. In this study, we found that acid leak-off mechanism in naturally fractured carbonates is much different from that in reservoirs without natural fractures. The leakoff volume is several times of nonreactive acid. Since the acid widened natural fractures, leakoff velocity increase with time firstly , then decrease. While the leakoff velocity of the nonreactive fluid decrease sustained. We also analyze other sensitivity parameters of the acid leakoff. In this model, we explain the acid leakoff mechanism in naturally fractured carbonates, and provide a more accurate calculating of fluid loss.

Abstract: On the basis of percolation mechanism for dual-porosity, an effective wellbore radius model in the dual-porosity was established, and the Laplace space solution could be obtained by solving this model. The solution had a similar structure and could be simplified into a unified expression in the different outer boundary conditions. The solution with a similar structure can avoid the complex calculations, it is beneficial to analyze the influence of various parameters on the solution in the dual-porosity model, and facilitate to master and use by engineering technicians.

Abstract: Sebei NO.2 gas field I-1 layer group is shallow-buried with comparatively lower formation energy. In the process of developing, the formation pressure drops and the total energy consumption of the gas-liquid two phase pipe flowing increases gradually, which leads wellbore to produce accumulated fluid that greatly reduces gas well productivity. This paper is based on the mastery of gas field reservoir characteristics and production dynamics, analyzing the changes of gas well production performance before and after gas wells with accumulated fluid. A wellbore liquid loading identification model of Sebei NO.2 gas field is established in terms of the liquid removing capacity calculations, wellhead characteristic observation method, the pressure gradient method. In the aspect of liquid loading volume, the study based on the theory of wellbore gas-liquid two phase flow, using four classical pressure distribution models to construct a combined model that is more suitable for single wells, analyzed the features of fluid gas well distribution with structural characteristics and other aspects. Practical application shows that the analysis results are reliable and highly practical, and deepening the understanding of the phenomenon of gas liquid loading.

Abstract: Junggar Basin is located in north Xinjiang and it has a huge amount of coalbed methane resources with less exploration and mining. The most vital characteristic in junggar basin is coal dip angel and gas content varies a lot in different areas. This paper reveals the relationship between gas content and coal seam dip angel, bigger the coal seam dip angel lower the gas content. The target area of CBM exploration and mining in junggar basin is HEGSH-STH area, HEGSHX area, BSMY-JJM area,LJM area, KLMY area, HSTLG area and XZJQ area. Gas content is mainly influenced by tectonic movement in junggar basin, it is low in complex structure area and high in simple structure area. Inclination of the coal seam stands for the complexity of the structure in junggar basin, the structure is complex when the coal seam is steep, it is simple when the coal seam is flat. The result can be used as a new method for coalbed methane exploration and development in inclined coal seam areas, small coal dip area should be chosen as the high gas content target.