致密砂岩气藏水平井多学科综合导向新技术——以鄂尔多斯盆地为例

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

鄂尔多斯盆地上古生界致密砂岩气藏的储层主要表现为近南北方向条带状展布,河道分叉、交汇频繁,单砂体接触方式以侧向加积形成的多层式接触为主,河流交汇处砂体具有近东西向横卧分布的特征,给水平井地质导向带来了很大的难度。为了提高水平井储层钻遇率,系统分析了水平井地质导向现状和储层沉积特征,利用三维地质建模与三维地震对储层空间展布进行预测,同时结合对已钻水平井砂体空间展布的认识,不断完善和丰富水平井地质导向技术与方法,形成了"小层精细对比入靶、地质小尺度、地震大方向"的多学科思维深度融合的综合导向新技术,并进行了现场应用。研究结果表明:①沉积模型导向可在入靶过程中精确制导,提高一次入靶成功率,是斜井段入靶导向的主要方法;②地质建模导向可指导水平井钻进,但与地下真实地质体存在着一定的误差,可作为水平段辅助导向方法;③三维地震导向可区分复合河道界限和判断优势砂体空间相对位置,对水平段导向有很好的预判和指导性,是水平段导向的主要方法;④新方法在致密砂岩气示范区应用于水平井62口,实现平均水平段长1 430 m、平均砂岩钻遇率86.2%、平均气层钻遇率70.2%,水平井气层钻遇率提高了10%以上。

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 geosteering of horizontal wells. In order to improve the reservoir drilling rate of horizontal wells, this paper systematically analyzed the geosteering 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 geosteering 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 judgement 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 1 430 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%.