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本文研究了采用乳化钻井液(油基钻井液OBM)所生成的粗乳液对胶结低渗至中渗砂岩地层的潜在伤害。使用了两类乳化钻井液:矿物油基钻井液和合成基钻井液。研究发现,测试用的OBM中的乳液可以由乳化剂稳定,也可以由固体颗粒(有机黏土和钻屑)所稳定。在低剪切速率下,在显微镜下可以观测到水滴和颗粒形成的聚集体。在瞬时滤失阶段,乳液侵入对油层的伤害最大,特别是当钻井液中的乳液不稳定时尤甚。乳液侵入的危害性将随着滤失压力的增加而增加。大量的现场试验发现,混合了钻井液滤液和储层流体的乳液的稳定性主要受乳化钻井流体和原油组分的影响。在90℃下进行岩心流动实验发现,乳液的存在会对地层造成严重伤害。在高温老化后伤害部分恢复。在90℃下,乳液在岩心中的稳定性要比在室内实验中的稳定性高。在高剪切速率下,在储层中形成乳液的可能性是最高的,如在瞬时滤失阶段和采油初期。随着钻井液和储层中乳化剂的增加,这种乳液形成的机率也增大。乳液造成的地层伤害是暂时性的。由于乳液是热力学不稳定体系,乳液造成的永久性伤害的可能性随着温度的升高而降低。因此,乳液的稳定和失稳机理主要由钻井液滤液和储层流体来决定。如果伤害区域被产出油扫过,用油稀释清除乳液的方法就有可能实现。在室内实验中使用合成油代替原油,会对乳液引起的潜在地层伤害评估不足。室内实验时间过短会对乳液造成的潜在地层永久性伤害评估过高。
In this paper, we investigate the potential damage of the coarse emulsion produced by emulsion drilling fluid (oil-based drilling fluid OBM) to the formation of low-permeability cemented sandstone formations. Two types of emulsion drilling fluids are used: mineral oil based and synthetic based drilling fluids. The study found that the emulsions in the test OBM can be stabilized by the emulsifier and can also be stabilized by solid particles (organoclay and drill cuttings). At low shear rates, aggregates of water droplets and particles can be observed under a microscope. In the instantaneous fluid loss phase, emulsion intrusion is most damaging to the reservoir, especially if the emulsion in the drilling fluid is not stable. The dangers of emulsion intrusion will increase with the increase of filtration pressure. Extensive field trials have found that the stability of emulsions mixed with drilling fluid filtrate and reservoir fluids is mainly influenced by emulsified drilling fluids and crude oil components. Core flow experiments at 90 ° C showed that the presence of the emulsion can cause serious damage to the formation. After high temperature aging damage part of the recovery. At 90 ° C, the stability of the emulsion in the core is higher than in laboratory experiments. At high shear rates, the possibility of forming an emulsion in the reservoir is the highest, as in the instantaneous filtrate loss and early recovery. As emulsifiers in drilling fluids and reservoirs increase, the probability of such emulsion formation increases. Formation damage caused by the emulsion is temporary. Since the emulsion is a thermodynamically unstable system, the likelihood of permanent damage from the emulsion decreases with increasing temperature. Therefore, the mechanism of emulsion stability and instability is mainly determined by drilling fluid filtrate and reservoir fluid. If the affected area is swept by the produced oil, it is possible to dilute the emulsion with oil. The use of synthetic oil instead of crude oil in laboratory experiments will not assess the potential formation damage caused by the emulsion. Too short an indoor lab will assess too much potential permanent formation damage from the emulsion.