Abstract:

Based on the current situation of stress direction change and its mechanism insufficiently understanding during oilfield development, anisotropic drilling from four cores in Chang-6 oil layer group of a block of Ansai oilfield in Ordos basin, stress direction relative change is measured respectively in dry sample and stratigraphic condition and analyzing the machanisms of effects. Results indicate that there is an obvious difference under the dry sample and stratigraphic condition, which suggests that it has an important meaning to test stress under in-situ condition. Maximum horizontal principal stress direction changes from 4.65° to 8.73° during oilfield development, the average is 7°, and analysis of characteristics of reservoir physical property and mechanism of rock fracture suggests that “natural channel” has an important control function to in-situ stress direction change. Combined with the initial in-situ stress direction, current stress direction of the study area is regarded as about NE58°. The conclusion does make crucial sense to oilfield reconstructive measure such as well network adjustment and artificial fracturing.

Key words: words Ordos Basin, low permeability reservoirs, Chang-6 oil layer group, stratigraphic condition, in-situ stress direction

摘要：
摘要 基于油田开发过程中对地应力方向变化及其影响机制认识不足的现状, 对鄂尔多斯盆地安塞油田某区块长6 油层组4 口取芯井各向异性钻柱, 分别在干样与地层原位条件下进行现今地应力方向相对油田开发初期地应力方向偏转值的测定, 并对其影响机制进行分析。结果表明: 干样与地层原位条件下测试的地应力方向变化存在较大差异, 因此对于油田储层地应力进行地层原位条件下的测试具有重要的意义; 在油田注水开发过程中最大主应力方向相对偏转值在 4.65°~8.73°之间, 平均值约为 7°, 从储层物性特征、岩石破裂机理等方面进行分析, 认为“天然水道”对地应力方向的偏转具有重要的控制作用; 根据油田开发初期地应力方向(NE65°), 确定研究区现今地应力方向约为 NE58°。研究结果对油田开发过程中水力压裂、加密布井以及井网调整等实际问题有重要指示意义。

关键词: 鄂尔多斯盆地, 低渗透油藏, 长6 油层, 地应力方向, 地层原位条件