鄂尔多斯盆地樊学油区长8砂岩裂缝平面展布及控制因素

The Planar Distribution and Controlling Factors of Sandstone Cracks in the Chang 8 Reservoir,Fanxue Oil District,Ordos Basin

裂缝发育程度及其平面展布是影响低孔特低渗储层有效、高效注水开发的关键。鄂尔多斯盆地樊学油区长8油藏及周边油藏投产油井存在砂岩裂缝发育区含水上升快、裂缝侧向油井水驱开发效率低等问题。本文基于岩心、声电成像测井资料标定常规测井资料,选取特征参数构建裂缝识别综合指数,实现樊学油区长8储层中砂岩裂缝的识别。依据识别结果绘制砂岩裂缝平面展布图,进而结合区域构造应力场及沉积特征分析裂缝发育的控制因素及其对生产开发的影响。研究表明,基底断裂中生代以来的重新活动控制了樊学油区裂缝的形成与展布,裂缝优势展布方位为北北西向和北东东向,砂岩裂缝的发育程度受区域构造应力场、砂体厚度以及岩层组合等因素影响。裂缝发育区油井具有初产高、产量递减快的特点,因此,在实际生产开发中,需要选择合适的注采井网,尽量采用大井距、小排距的方式提高驱油效率。上述认识为油藏开发部署提供一定的参考。

The development degree and plane distribution of cracks are the key to effective and efficient waterflooding exploitation of low porosity and ultra-low permeability reservoirs.There exist problems in the production wells of Chang 8 reservoirs,Fanxue oil district and its surrounding reservoirs,such as rapid water rising in the sandstone area with well-developed cracks,and low water flooding mining efficiency of the fractured lateral wells.This study is based on cores and acoustic-electric imaging to calibrate conventional logging,and selects characteristic parameters to construct a comprehensive crack identification index to recognize sandstone cracks in Chang 8 reservoirs of Fanxue oil district.In terms of the identification results,a plane distribution map of sandstone fractures is prepared,and then the controlling factors of crack development and its impact on production and exploitation are analyzed in combination with the regional tectonic stress field and sedimentary characteristics.The study shows that the reactivation of basement faults since Mesozoic has controlled the formation and distribution of cracks in the Fanxue oil district,the dominant distribution of fractures is in NNW and NEE directions,the development degree of sandstone cracks is affected by factors such as regional tectonic stress field,sand body thickness and rock-layers combination.Considering that the oil wells in the crack development zone have high initial production and rapid production decline,so the actual production and exploitation should choose an appropriate injection-production well network and adopt large well spacing and small row spacing as much as possible to enhance oil displacement efficiency.These perceptions provide a reference for the next development and deployment of the reservoirs.