委内瑞拉疏松砂岩水平井弱凝胶微泡钻井液

委内瑞拉东南部的奥里诺科重油带AYACUCHO区块MFM构造分区块油层具有油藏浅、压力低、孔隙度大和井温低等特点。该区块多为水平井,且井段较长,以往混油聚合物等常规水基钻井液在施工过程中经常发生上提拉力过大、下放遇阻、卡钻等事故复杂。针对常规水基钻井液的不足,自主研发了流型调节剂和发泡剂,形成了一套弱凝胶微泡钻井液配方,体系的密度在0.85~1.00 g·cm-3范围内可控,120℃老化后低剪切速率黏度保持40 000 mPa·s以上,有效解决了常规水基钻井液在施工过程中容易发生上提拉力过大、下放遇阻、易卡钻的难点。该体系在MFM-62井、MFM-65井进行了现场应用,水平段均一次性顺利钻完,无事故复杂,水平段钻进周期从12 d降至4 d,口井日产量达90 t,较邻井提高40%以上。 

Study and Application of a Weak Gel Micro Foam Drilling Fluid in Horizontal Wells through Loose Sand in Venezuela

The reservoir formations in MFM sub-block of the block Ayacucho in the Orinoco heavy oil belt, southeast Venezuela, are characteristic of shallow depth of burial, low pressure, high porosity and low bottom hole temperature. Wells drilled in this block were mostly horizontal wells with long intervals. In previous drilling practices, water base polymer muds mixed with oil were commonly used, resulting in downhole troubles such as over-pull and resistance during tripping, and pipe sticking etc. A weak gel micro foam drilling fluid formulated with a flow pattern optimizer and a foaming agent has been developed in place of the water base polymer muds previously used. This weak gel micro foam drilling fluid has a density between 0.85 g·cm-3 and 1.00 g·cm-3. The low-shear-rate viscosity of the drilling fluid after being aged at 120℃ is at least 40 000 mPa·s. With this drilling fluid, problems found in the past, such as over-pull and resistance during tripping and pipe sticking, were effectively resolved. Application of the weak gel micro foam drilling fluid on the well MFM-62 and the well MFM-65 was successful; the horizontal sections of the two wells were successfully drilled, with no downhole troubles occurred. Time spent drilling the horizontal sections was reduced from 12 d to 4 d. Daily oil production rate was 90 t, 40% higher than that of the adjacent wells.