地质科技通报 (Jul 2022)
Shale gas horizontal well geosteering technologies and countermeasures research in narrow and steep syncline formations of northern Guizhou area
Abstract
Northern Guizhou area is located at the edge of the Sichuan Basin, and its structure belongs to Wuling fold area. Wufeng Longmaxi shale stratum is in a series of narrow and steep residual synclines, and the main developed shale stratum is within five meters of the bottom of the Longmaxi Formation, with a thin thickness. Due to the complex surface and underground geological conditions, the seismic velocity changes in this area, and the horizontal and vertical changes in various geological factors, such as the stratum dip angle and thickness, are large, so the drilling rate of horizontal wells in this area is relatively low. In this paper, the difficulties encountered in horizontal well geosteering in the narrow and steep residual syncline are sorted, and the modelling of velocity, structure, thickness, dip angle and curve was carried out. Combined with the element change law and element imaging technology, the track while drilling horizon was identified step by step to improve the hit target rate and drilling encounter rate. The actual drilling results show that the deviation from the geological design was reduced within 25 meters, the drilling encounter rate of high-quality shale was increased to 99.2%, and the drilling encounter rate of the box was increased to 96.5% from 87.6%. Three wells of them achieved the geosteering achievements of hit rate 100%, high-quality shale encounter rate 100%, and box body encounter rate 100%. In areas similar to the narrow and steep residual syncline geosteering difficulty in the northern Guizhou area, the application of this set of technical countermeasures can avoid subtle structural changes such as small folds in time and effectively ensure the box drilling rate of horizontal wells, which can provides solid technical support for horizontal well geosteering.
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