The Earth Stress Interpretation Software Design Of Compact Gas Reservoir In Western Sichuan Depression

The research of earth stress has been widely used in many petroleum engineering areas, and it has become a necessary basic data in which the oil and gas reservoir engineering, the oil and gas exploration, the drilling and completion wells and the program design of oil and gas production engineering, and it is important to various aspects which the evaluation of wellbore stability during drilling well, the prediction of burst pressure, and the prediction and prevention of damaged oil and water well casing. Furthermore, with the rapid increase of gas requirements, many countries have attached importance to the exploration and development in compact sandstone gas reservoir. It was base on the research of earth stress that the wellbore instability, hydraulic fracture and other technology often happened in compact sandstone gas reservoir.In this thesis, we take the Xujiahe Formation of Xinchang area in Western Sichuan depression as an example. According to theories and methods in many kinds of subjects as petroleum geology, structural geology, geophysical well logging, reservoir geology, rock mechanics, drilling engineering and so on, begin with an analysis on character of rock mechanics, we carry out many researches such as the rock mechanics trial, interpretation of earth stress, establishment of three major stress, prediction of fracture pressure and collapse pressure. However, researches on the earth stress software design are scare in higher education institutions in China. Therefore, according the theories above all, we developed the earth stress interpretation visual windows software on Visual C++6.0 platform. This software not only integrated a large number of achievements of the former research, but also provided different mathematical methods for users to create new model for different area. In the application of study area, we have achieved good results by using the earth interpretation software.Firstly, according to the previous finding, which include velocity of transversal wave and information of each well, we can select three log parameters, such as CNL, RT, AC, which have the most affect on the wave velocity of rock samples by the mathematical method called optimal subset regression, short for OSR. Then introduced the partial least-square regression (GA-PLS) to fit the parameters, and building the model of shear wave calculation, which provided a reliable foundation for the next research. In this way, proper models were used to calculate elastic parameters and strength parameters of rocks for special features of the study area. Experimental data were corrected calculation data by the transformation model. Finally, the reliable result was obtained.Secondly, base on the principle of getting AC data of compaction curve, we established the compaction curve of study area, which provided a reliable data for computing formation pressure, and interpreted formation pressure by using the Eaton method. Additionally, in this thesis, we used the BP neural network to predict formation pressure, compare with the traditional method. We find that BP neural network make a better consequence than Eaton method. Besides, we research that calculation of the three axis stress through by HPF, AES and ADS, choose ADS to compute earth stress of study area, and obtain the vertical earth stress by adding the weight of above rock instead of integration of density function. By this way, we established the profile of single well and safe mud weight window, and the safe density of mug window.Moreover, a computational earth stress interpretation software was developed on Visual C++6.0 platform by using MFC to visual program. This software consisted of the rock mechanical parameters calculation module, the interpretation of earth stress module and single well curve drawing module. The rock mechanical parameters calculation module carried out that the horizontal wave calculation which include formulas invent by Eberhart-Philips(1989), GanLideng(1990), LiQingzhong(1992), and ZhouWen(2009); the shale content calculation; the elastic, such as possion rate, elasticity modulus, shear modulus, bulk modulus and so on, were computed by the popular formulas invent by Miller and Deere, McNally(1987), ZhouWen(1998), Horsrud(2001), WangYuan(2005) and so on. Strength parameters were calculated by the model which we established for study area because of its complex condition by the software we designed in this research. The corrective model between static data and dynamic data was offered by this software too. Besides, the interpretation of earth stress module can calculate formation pressure, the three principal earth stress, fracture pressure and collapse pressure. This software included 8 formulas of earth stress, 2 formulas of collapse pressure, and 13 formulas of burst pressure. Then, single well curve drawing module can obtain the single well curve through linking the other professional drawing software such as Carbon software and Forward software. At last, comprehensive earth stress interpretation software was born.