A new multi-disciplinary integrated steering technology for horizontal wells in tight sandstone gas reservoirs: A case study of the Ordos Basin

Abstract

The sandstone layers of the Upper Paleozoic tight clastic gas reservoirs in the Ordos Basin are generally distributed in a pattern of nearly NS strip, and the channel branches and intersects frequently. A single sand body is in a multilayered contact mode resulted from lateral accretion, and the sand bodies at the river intersections present a feature of lying in the nearly EW direction, which brings great difficulties to the geo-steering of horizontal wells. In order to improve the reservoir drilling rate of horizontal wells, this paper systematically analyzed the geo-steering status of horizontal wells and the sedimentary characteristics of reservoirs. Then, the spatial distribution of reservoirs was predicted using 3D geological modeling and 3D seismic. In addition, based on the cognitions on the space distribution of sand bodies from the drilled horizontal wells, the horizontal well geo-steering technology and method were constantly improved and enriched. Thus, an integrated steering technology of “fine sublayer correlation for target entering, geology in small scale, and seismic in large scale” based on in-depth integration of multidisciplinary thinking was newly formed, and it was also applied on site. And the following research results were obtained. First, under the guidance of the sedimentation model, the target entering process is controlled precisely and the success rate of one-trip target entering is improved, so it is one important method for the target steering of deviated hole sections. Second, geological modeling can guide the drilling of horizontal wells, but to some extent, it is deviated from the real underground geologic bodies, so it can be used as an auxiliary horizontal-well steering method. Third, 3D seismic steering can tell the boundary of complex river channel and discriminate the spatial relative location of predominant sand bodies, so it is the primary method for horizontal-well steering to provide excellent judgment and guidance on the steering of horizontal hole sections. Fourth, owing to the application of this new method in 62 horizontal wells drilled in the tight gas demonstration area, the average horizontal section length reaches 1430 m, the average sandstone drilling rate is 86.2%, the average gas layer drilling rate is 70.2%, and the gas layer drilling rate of horizontal wells is increased by more than 10%.