Research On Borehole Stability Of Shale Gas In Pengshui、Huangping Block

Due to the high density and low permeability of shale gas reservoirs, the large-scale production and commercial use of shale gas development has been facing technical bottleneck problem, in development use exceptional well such as directional well extended reach well to enhance oil recovery, but the complexity of well types and the particularity of geological conditions had decided the difficulty of process of shale gas drilling. In well drilling process,the wellbore stability problem is the the most critical and most concern, which largely determines the safety and cost of a well.As the same as conventional oil and gas resources, the most of borehole wall instability problem of shale gas resource in the course of drilling are also mud shale problem. The open hole broken the original formation stress balance, only with the appropriate drilling fluid density to maintain wall stability, but in the process of drilling fluid circulating, filtrate will seep into formation,to reduce the intensity of the wall rock. Moreover, because of the bedding and strong water sensitivity of mud shale, in a period of the after the hole formation,will creat a substantial collapse, causing resistance, suppress pump even hole abandonment, will have an affect on the whole shale gas exploration and development process.This paper is based on Pengshui and Huangping these two shale gas block as research object to carry on shale gas horizontal well borehole stability research. This region has the feature of bigger stratigraphic dip, more percolation layers, higher percolation speed, and borewall denudation collapse and reducing sticking happen from time to time, thus seriously affecting the drilling cost and economic benefit. Therefore, this paper aims at these questions during the drilling process in this region, specially making the following research:(1) Formation rock characteristic research. Launching rock mechanics properties and permeability tests, testing the formation rock strength stress parameters and permeability of the main target stratums in this region and combining with log data, we establish the rock mechanics parameters section. Using the X-ray quantitatively describe the hydrosialite grain lineation order along bedding surface, so as to study the structure of the shale. (2)Ground stress profile is determined. To develop Kaiser test for ground stress test. Through the ground stress calculation model, we can use well logging data to calculate ground stress profile and in depth analysis huangping and pengshui two shale gas block, which mainly shale objective interval of the maximum principal stress, the minimum principal stress, the vertical stress of the longitudinal distribution regular pattern.(3) Wellbore stability is analysed. According to well trajectory condition, in the analysis of the stress state of surrounding rock on the wall, combining with the failure criterion of rock strength, establishes the formation collapse pressure and fracture pressure calculation model, analyses the relationship between different wellbore direction, inclination and wellbore stability in shale gas Horizontal wells, puts out the best borehole drilling direction.(4) The safe drilling fluid density window is determined. With the foundation of wellbore stability analysis, The horizontal well drilling fluid density window is proposed in Huangping, Pengshui two shale gas blocks.