低渗透油田重复压裂技术研究

Refracturing techniques for low permeability oil fields.

低渗透油田的重复压裂被广泛重视，但国内外普遍存在复压成功率低、增产效果差、有效期短的问题。在实施整体压裂投产的某特低渗透油田复压油藏工程、优化设计和现场试验研究中，初步建立了一套重复压裂研究与实施方法。初次压裂裂缝导流能力随开发时间增长而下降，将这一规律用于复压油藏数值模拟；根据数模结果，应优先选择剖面上动用程度差、未见水或低含水且地层能量充足的小层进行复压；产量优化缝长（其界限约７０ｍ）与含水、地层渗透率无关，应根据油藏开发动态特征和地层非均质性确定具体复压井的缝长。根据油藏特性和复压工艺特点优化设计，选用有机硼交联改性瓜尔胶压裂液和低密度的支撑剂，施工排量约５ｍ３／ｍｉｎ，以斜坡方式连续提高砂液比（１０％～６０％），前置液百分数约６０％。这些优化设计结果提高了复压的工艺可行性。对４口井进行重复水力压裂先导性试验，施工成功率达１００％，压后５ｍｏｈｔｈ持续有效，阶段累计净增产原油８４４０ｔ，含水稳定或下降，取得了显著的增产效果和经济效益。

Refracturing low permeability oil fields has received extensive attention both at home and abroad. However, a lot of problems are observed, such as low success ratio, inferior stimulation results, and short effective period etc.. In carrying out the refracturing operations in an oil field which is put on production after field wide fracturing, a set of method of studying and operation was set up preliminarily. Flow conductivity of fractures from the initial fracturing job will decrease as production continuous, and this regularity is considered in the numerical reservoir simulation after refracturing; Based on the results of simulation, less produced, no water cut or low water cut, and having enough energy intervals (single pay zone i.e. with better results of pressure maintenance, should be selected as candidates for repressuring. Fracture length should be optimized by taking the characteristics of well behavior and the heterogeneity into consideration (a limiting value of about 70cm will be a limiting case). Based on the reservoir characteristics and technological conditions the refracturing design is optimized. Modified guar gum crosslinked by organic boron agent and low density oriental haydite were selected as proppants in a refracturing job. Flow rate selected is 5m 3/min, and sand/liquid ratio rose gradually from 10% to 60%, and a prepad of 60% were used. These optimized design increases the feasibility of the refracturing technology pilot tests including the refracturing of 4 wells show a success ratio of 100%, and the stimulation results have lasted for 5 months with a total period of induction increase of 8440t, and stable or decreased water cut. Significant stimulation increase and economic benefit were obtained. Subject