也门裂缝性基岩油气藏钻井液技术

Drilling fluids for fractured basement reservoir in Yemen

也门基岩的孔隙度和渗透率低，裂缝是其主要油气渗流通道，多采用大斜度定向井和水平井开发，井漏是钻井面临的主要潜在风险，固相颗粒侵入是油气藏损害的主要因素。室内通过对比固相含量和动塑比，筛选出加重剂氯化钠和碳酸钙，流型调节剂Duo．Vis，进而优选出2种无膨润土钻井液配方，密度范围1．01—1．40g／cm^3，动塑比1．0～2．0Pa／mPa·s。另外，针对漏失问题，提出了几种防漏堵漏技术，一是用酸溶性的桥堵剂暂堵；二是用化学交联堵漏浆或是触变性水泥浆封堵：三是以可循环无固相微气泡（Aphron）钻井液作为备选钻井液，满足低压地层钻井需要。也门基岩钻井液流变性能优良，处理剂能够完全酸溶或水溶，具有低固相或无固相的特点，对油气藏伤害轻微。现场应用32口井，包括9口水平井，取得了较好的应用效果。

The rocks are hard with very low matrix porosity and permeability in Yemen fractured basement reservoir. The main flow channels of oil and gas are fractures. For getting high daily production, the deviated and horizontal wells were drilled. During drilling operations, lost circulation was the main potential downhole hazard, and solid particle invasion was the main formation damage factor. By comparing the solids concentration and the ratio of yield point to plastic viscosity （YP/PV）, sodium chloride and calcium carbonate were selected as weighting agents, and Duo-Vis was selected for viscosifier. As a result, two kinds of bentonite-free drilling fluids were developed with the mud weight range of 1.01-1.40 g/cm3 and the YP/PV range of 1.0-2.0 Pa/mPa-s. For preventing and stopping the lost circulation, some techniques were proposed, among which the first one was temporary sealing with acid soluble bridge blinding material, and the second one was permanent sealing with chemical cross-linked slurry or thixotropic cement slurry. Furthermore, Aphron was a backup drilling fluids for extreme low pressure formation. The drilling fluids for Yemen basement formations had good theology and the additives were totally acid soluble or water soluble, so they contained low solid concentration or even no solid, resulting in slight or no reservoir damage. The fluids were successfully used in 32 wells, including 9 horizontal wells.