致密气藏砂岩空间发育模式对水平井产能的影响

Influence of sandbody development pattern on horizontal-well productivity in tight gas reservoirs

水平井开发技术已成为鄂尔多斯盆地上古生界致密砂岩气藏的主要开发手段。基于已完钻井地质资料大数据,构建空间地质模型,分别为切割连通型、冲刷连通型及孤立型。水平井开发之初,切割连通型储层为主要目标,多实施平直型水平井。随着开发的深入,为完善井网、提高储量动用程度,针对冲刷连通型和孤立型储层的大斜度型水平井和阶梯型水平井的比例逐渐增加。为了明确研究区砂体发育模式对水平井生产能力的影响,利用试气成果、生产曲线等动、静态资料,对水平井的生产能力进行分析评价。研究结果表明:(1)与空间地质模型对应的水平井轨迹类型为平直型、大斜度型、阶梯型;(2)3种类型水平井均具有一定稳产能力(>2000 d),其中平直型和大斜度型水平井显示出较好的稳产能力,阶梯型水平井稳产能力有限,但仍不失为区块效益开发的必要补充;(3)建立区块水平井类型的单位套压采气量与累计采气量的拟合关系,可对区块阶段性产量和稳产能力进行预测,为区块规划提供依据。

Horizontal-well development emerges as a key technique for the Upper Paleozoic tight sandstone gas reservoirs,Ordos Basin.Based on big data about geological information of the drilled wells,geological models have been constructed from aspects of various spatial types,like cutting-connected,erosion-connected and isolated reservoirs.Straight horizontal wells are usually employed at the beginning of the horizontal-well development with cut-connected reservoirs as the main target.Following the additional exploitation process,the quantity of both highly deviated and ladder-type horizontal wells individually for erosion-connected and isolated reservoirs is increasing to perfect well pattern and raise reserves’producing degree.Thus,in order to clarify the influence of sandbody development pattern on horizontal-well productivity in the study area,this productivity was analyzed by using dynamic and static data such as gas testing findings and production curves.Results show that(i)there exist three horizontal-well trajectories corresponding to the geological models,including straight,highly deviated and ladder types;(ii)these three types have a certain stable production capacity beyond 2,000 days among which the straight and highly deviated ones exhibit a better stable capacity,while a limited stable capacity for the ladder type but still as an essential supplement for the beneficial development;and(iii)through the established fitting relationship of gas production per unit casing pressure to cumulative gas production,both periodic gas production and stable productivity in the block can be predicted for these types of horizontal wells to provide basis for block planning.