Engineering Quality Study Of Shale Gas Reservoir

Nowadays because of the rapid development of world economy and the growing consumption of energy, conventional oil and gas resources will be increasingly difficult to meet the demand of international energy. For this reason, unconventional oil and gas resources get more and more attention. As one kind of unconventional oil and gas resources, the shale gas has advantages of wide gas-bearing area, large amount of resources, long productive life and stable production, which make it ho direction of global exploration and development. Besides the characteristics of shale gas reservoir such as low porosity, low permeability, self-production and self-storage, compared with conventional gas reservoir, the reservoir forming mechanism and evolution of distribution are obviously different from conventional gas reservoir. All above make it more difficult for exploration and development of shale gas. The retrofit fracturing technology is usually used for production increase.Through effective logging evaluation method, logging data can be used to make qualitative identification or quantitative evaluation of rock mechanics parameters of shale gas reservoir in order to provide necessary information for evaluation of resources and late development. The core content of this paper is the research of calculation of rock mechanics parameters in quantitative evaluation of shale gas reservoir. Basing on the study result of rock mechanics parameters, the study about explanation of crustal stress and evaluation of borehole wall stability can be made.Referring to qualitative identification of shale gas reservoirs, the conventional logging response characteristics generally has the characteristics of high gamma, high neutron, high acoustic time, high resistivity, low density and low photoelectric effect. Quantitative evaluation of shale gas reservoir engineering quality parameters includes poisson ratio and young’s modulus, shear modulus, brittleness index and so on.Shale gas reservoirs are usually tight. Hydraulic fracturing is always necessary in the later development period. Accurate evaluation for rock mechanics parameters of shale gas reservoir has an important guiding significance to hydraulic fracturing. By using logging data of P-wave and S-wave to calculate rock mechanics parameters, we can find that these rock mechanics parameters have a good consistency in explaining the mechanical properties of rock. They can be used to guide the engineering development of shale gas. In addition, the explanation and the analysis of characteristics of formation pressure are based on this.Shale gas reservoirs are usually low porosity and low permeability. The brittleness characteristic of shale gas reservoir has an important influence on the development effect of shale gas. The brittle shale is beneficial to the growth of natural fracture and forming mesh complex fracture with capacity of diverting after fracturing, which can increase the production of shale gas. There are two main methods in the actual production. The one is to take advantage of mineral content of shale to study the brittleness of shale, namely mineral brittleness evaluation. The other one is to use time difference from logging data between P-wave and S-wave and density to calculate rock poisson’s ratio and young’s modulus in order to evaluate the brittle of rock, namely elastic modulus of brittle evaluation.Although the two methods can both evaluate the rock brittleness, there is a lot of limitations in practical applications. The former requires chemical elements logging data, and the latter requires array acoustic logging data or dipole shear wave logging data. However, not every well has these special logging data. Thus, conventional logging data should be made full use of to establish the correlation of mineral brittleness and themselves so as to accomplish the evaluation of rock brittleness.Basing on the above method, the author programmed an reasonable and complete software for evaluation and analysis including the calculation methods and models of rock mechanical parameters, isotropic crustal stress and anisotropic crustal stress. According to the shale gas section with qualitative identification, the engineering quality study of shale gas reservoir was made. The data processing result of X-1 well and X-2 well were basically consistent with shale strength property evaluation scope. Thus, it means that the software can play a guiding role in actual exploration and development.