The generalized method for estimating reserves of shale gas and coalbed methane reservoirs based on material balance equation

As the main unconventional natural gas reservoirs,shale gas reservoirs and coalbed methane(CBM)reservoirs belong to adsorptive gas reservoirs,i.e.,gas reservoirs containing adsorbed gas.Shale gas and CBM reservoirs usually have the characteristics of rich adsorbed gas and obvious dynamic changes of porosity and permeability.A generalized material balance equation and the corresponding reserve evaluation method considering all the mechanisms for both shale gas reservoirs and CBM reservoirs are necessary.In this work,a generalized material balance equation(GMBE)considering the effects of critical desorption pressure,stress sensitivity,matrix shrinkage,water production,water influx,and solubility of natural gas in water is established.Then,by converting the GMBE to a linear relationship between two parameter groups related with known formation/fluid properties and dynamic performance data,the straight-line reserve evaluation method is proposed.By using the slope and the y-intercept of this straight line,the original adsorbed gas in place(OAGIP),original free gas in place(OFGIP),original dissolved gas in place(ODGIP),and the original gas in place(OGIP)can be quickly calculated.Third,two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software,respectively.Finally,two field studies in the Fuling shale gas field and the Baode CBM field are presented.Results show that the GMBE and the corresponding straight-line reserve evaluation method are rational,accurate,and effective for both shale gas reservoirs and CBM reservoirs.More detailed information about reserves of shale gas and CBM reservoirs can be clarified,and only the straight-line fitting approach is used to determine all kinds of reserves without iteration,proving that the proposed method has great advantages compared with other current methods.

Application of integrated formation evaluation and three-dimensional modeling in shale gas prospect identification

Identifying the shale gas prospect is crucial for gas extraction from such reservoirs.Junggar Basin(in Northwest China)is widely considered to have high potential as a shale gas resource,and the Jurassic,the most significant gas source strata,is considered as prospective for shale gas exploration and development.This study evaluated the Lower Jurassic Badaowan Formation shale gas potential combined with geochemical,geological,and well logging data,and built a three-dimensional(3D)model to exhibit favorable shale gas prospects.In addition,methane sorption capacity was tested for verifying the prospects.The Badaowan shale had an average total organic carbon(TOC)content of 1.30 wt.%and vitrinite reflectance(Ro)ranging from 0.47%to 0.81%with dominated type III organic matter(OM).X-ray diffraction(XRD)analyses showed that mineral composition of Badaowan shale was fairly homogeneous and dominated by clay and brittle minerals.67 wells were used to identify prospective shale intervals and to delineate the area of prospects.Consequently,three Badaowan shale gas prospects in the Junggar Basin were identified:the northwestern margin prospect,eastern Central Depression prospect and Wulungu Depression prospect.The middle interval of the northwestern margin prospect was considered to be the most favorable exploration target benefitted by wide distribution and high lateral continuity.Generally,methane sorption capacity of the Badaowan shale was comparable to that of the typical gas shales with similar TOC content,showing a feasible gas potential.

Development Strategy and Countermeasures of China's CBM Industry under the Goal of “Carbon Peak and Neutrality”

China’s coalbed methane(CBM) industry is in an extremely important “climbing period” and “strategic opportunity period”,which can be generally characterized by “three low and one small”:low degree of exploration and development,low adaptability of main technology,low return on investment and small development scale.Under the “carbon peak and neutrality” background,the development status of CBM industry is systematically combed.The resources,technology,management problems and reasons are analyzed.Strategies and countermeasures to accelerate the industrial development are put forward according to the factors such as efficient development of resources,major technical breakthrough,talent team training,policy formulation and implementation,return on investment and so on.The existing problems are as follows:(a) The overall occurrence conditions in China are complicated and the development is difficult compared with the other countries.(b) The research precision accuracy of CBM resource conditions is not enough.(c) The adaptability of technology is poor.(d) The management mode is not suitable.In view of these problems,this paper puts forward the “two steps” development strategy and the technical and management countermeasures of “five in one”.The corresponding “five in one” technology and management countermeasures are the formulation and implementation of relevant safeguard measures in accordance with the principle of collaborative innovation in five aspects:resources,technology,talents,policies and investment.Through the above measures,the dream and grand blueprint of CBM industry shall be realized.

Numerical simulation of bubble plumes in overlying water of gas hydrate in the cold seepage active region

To study the seismic responses produced by gas hydrate bubble plumes in the cold seepage active region, we constructed a plume water body model based on random medium theory and acoustic velocity model of bubble medium. The plume water body model was forward simulated by finite difference. Seismic records of single shot show the scattered waves produced by the plume. The scattered wave energy is strong where the plume exists. Where the scattered wave energy is stronger, the minimum of travel time is always above the plume, which has no relationship with the shot's position. Seismic records of shot gathers were processed by prestack time migration. The migration section shows that the scattered waves produced by plumes can be imaged distinctly with higher accuracy. These researches laid a foundation for further study on the seismic responses produced by plumes and provided a new approach for the identification of gas hydrate.

Optimization of fracturing parameters for tight oil production based on genetic algorithm

It is difficult to determine the main controlling factors of tight oil production.In addition to the problem of uncontrollable prediction accuracy,the numerical prediction model established by the main controlling factors will also make the correctly predicted low production samples lose the value of development.Applying the optimization algorithm with fast convergence speed and global optimization to optimize the controllable parameters in the high-precision numerical prediction model can effectively improve the productivity of low production wells with timeliness,and bring greater economic value while saving development cost.Using PCA-GRA method,the sample weight and the weighted correlation ranking results of parameters affecting tight oil production were obtained.Thereupon then the main controlling factors of tight oil production were determined.Then we set up a BP neural network model with by taking the main controlling factors as input and tight oil production as output.The prediction effect of the network was good and can be put into use.The results of sensitivity analysis showed that the network was stable,and the total fracturing fluid volume had the greatest impact on the production of tight oil.Finally,by using genetic algorithm,we optimized the fracturing parameters of all low production well samples in the field data.Combined with the fracturing parameters of all high production well samples and the optimized fracturing parameters of low production wells,the optimal interval of fracturing parameters was given,which can provide guidance for the field fracturing operation.