Application Of HDIL In The Evaluation Of Tight Sandstone Reservoirs In Sulige Area

Tight sandstone gas resource is very rich in China. The gas reservoir in Sulige area is the largest tight sandstone gas reservoirs in China until now, and of great significance in the unconventional natural gas exploration field. This kind of gas reservoir has strong heterogeneity, complex micro pore structure and poor effective sand body connectivity. These characters lead the percolation mechanism of gas reservoir in Sulige area with low porosity and low permeability to be different from conventional gas reservoir. Thus the log responses are complex. Coupled with the impact of fracturing measures on the formation brought a series of challenges to the productivity’s prediction.High resolution array induction logging instrument(HDIL) has high vertical resolution and multiple radial detection depths, so that it has strong ability to distinguish thin layer and describe mud invasion profile. Through a series of log data processing, the influence of borehole, shoulder beds and mud invasion can be eliminated.Based on the tight sandstone gas layer of Shihezi 8 in the Permian(P?h), this study makes full use of the advantage of HDIL’s resistivity curves of different radial detection depth under a same vertical resolution which can precisely describe complex mud invasion profile. The tight sandstone reservoir evaluation methods were studied, including establishment of the forward model, the total difference parameter of resistivity curves, the fluid identification model and post-frac productivity forecasting model.This thesis carried out the study of the tight sandstone reservoir characteristics from the macroscopic geological view and the mineral content influence on productivity from microcosmic view. HDIL resistivity curves’characteristics of the tight sandstone reservoir also were analyzed.Based on the theory of induction logging system with double coil, the thesis introduced the measurement principle and structure of HDIL. Then the application scopes of Doll geometrical factor and other geometrical factors theories were analyzed. The focus of the thesis was the HDIL’s longitudinal and radial detection features. After log data preprocessing, a total of 18 log curves which contain 6 different radial detection depths and 3 vertical resolutions can be got. The six curves whose vertical resolution is 2in were the focus of this study. Finally Gianzero geometrical factor was used to analyze the mud invasion influence on HDIL’s resistivity curves."Core calibrate logging" method was used to establish porosity model by carrying out the multiple linear regression of core porosity and log curves. Porosity model and SVR method were used to establish permeability calculation model, and the SVR method’s precision was higher. Archie formula and experimental analysis data were used to calculate water saturation.The response difference between dual lateral logging and HDIL was used to set up the cross-plot to identify fluid properties. The total difference parameter of resistivity curves defined by HDIL resistivity curves’changing characteristics also was used to set up cross-plots and Bayes discriminant model for identifying fluid properties. Under the condition which hasn’t HDIL, the relationship between HDIL and other conventional logging was found by using the multiple nonlinear regression method and the estimates of the array induction logging resistivity curves can be got. This method solved the problem that conventional logging technology and interpretation methods can’t identify fluid accurately in tight sandstone reservoir.On the basis of analysis of the relationship between the logs, fracturing parameters and post-frac productivity, this thesis used gray correlation analysis method to calculate the correlation between each factor and post-frac productivity to elect the main factors which influence post-frac productivity. GA-Elman network was used to establish the post-frac productivity prediction model of tight sandstone reservoir in Sulige area. For commingled production layer. KHK. method was used to split productivity to each single point. Finally, this thesis analyzed the distribution characteristic of the gas and water productivity and realized the evaluation of tight sandstone reservoir of P2h in Sulige area.In summary, according to the complex characteristic of tight sandstone reservoir, this thesis take advantages of conventional logging and HDIL to improve the precision of tight sandstone reservoir evaluation. It has high application value.