大牛地致密砂岩气田水平井钻完井技术

Drilling and completion technology for horizontal wells in Daniudi tight sandstone gas reservoirs

鄂尔多斯盆地大牛地气田气藏类型多为低孔低渗砂岩气藏,水锁是气田的主要伤害因素,采用直井配合后期改造虽基本满足了相对高产区产能建设要求,但上述方法在新区不能有效建产,致使占气田近1/3探明储量的下二叠统下石盒子组盒1段气层不能有效动用,采用水平井技术可能是最佳选择。为此,在分析前期水平井钻井存在问题的基础上,优化细化了水平井方案设计,水基微欠平衡、近平衡水平井试验取得突破性进展,初步形成了水平井近平衡钻完井技术,欠平衡水平井钻井工艺在该区初见成效:在下二叠统山西组1—2段(山1—2段)、盒3段等一类气层实现了近平衡自然建产,在盒1段等三类气层实现了欠平衡自然建产。试验成果为有效动用该区探明未动用天然气储量提供了技术支撑。

Sandstone gas reservoirs in the Daniudi Gas Field of the Ordos Basin are of low porosity and low permeability and water-locking is one of the main threatening damages to this gas field.Stimulation measures adopted in the vertical wells there made it possible for the developed reservoirs to obtain a relatively high productivity,but in the succeeding development of this field,those previous stimulation measures were found to be helpless in the newly developed reservoirs.Especially the Lower Permian gas zone of He 1(the first member of the Lower Shihezhi Formation),which contains about 1/3 of the proved gas reserves of this gas field,could not be effectively developed,so horizontal well drilling had to be better adopted then.In view of this,based on an analysis of previous problems in horizontal well drilling,the horizontal well drilling scheme is optimized in every detail,and the breakthrough is made on the tests of aqueous slight underbalanced drilling and near balanced drilling of horizontal wells.Thus,a near-balanced horizontal well drilling and completion technology is developed and its application has shown initial success.Near-balanced natural production is obtained at the type-Ⅰpay zones like Shanxi 1-2(the first to the second member of Shanxi Formation) and He 3(the third member of the Shihezhi Formation) and the underbalanced natural production obtained at the type-Ⅲ pay zone like He 1.These above conclusions provide technical support for achieving more commercial gas flow from the explored untouched gas reserves in this field.