Experience Using Microbubbles-Aphron Drilling Fluid in Mature Reservoirs of Lake Maracaibo

The objective of the paper is to present field results obtained through the evaluation of the Micro-bubble Aphron system, as the drilling fluid in wells VLA-1321, VLA-1325, VLA-1326, VLA-1327, VLA-1329, VLA-1331, VLA-1332, VLA-1334 and VLA-1335 (wells corresponding to Lagomar Integrated Laboratory). This fluid does not require equipment such as compressors, rotary wellhead, equipment to generate and/or inject nitrogen and permits the taking of electric logs conventionally. During drilling, mud weight varied between 6.8 to 7.9 ppg and very low-pressure zones were run through, with equivalent gradients oscillating between 2.4 ppg and 6.4 ppg, without any problems of loss of circulation. The micro-bubble fluid presented excellent inhibition values to clay and shale since the Miocene sands of Basal La Rosa and the alternating sand and shale of the Eocene reservoirs were drilled without any problems. Moreover, in well VLA-1321, this lithology was with an exposure time of 25 days, without any instability problem. On the other hand, in wells VLA-1329, VLA-1331, VLA-1332, VLA-1334 and VLA-1335 all the intervals were drilled from 1520’ to 6900’, without using intermediate casing and without great problems, which cut down drilling time to 31.0 days with a saving of 4.7 MMUS$ for the corporation. It should be pointed out that the fluid has presented rheological properties , which have permitted drilling with excellent hole cleaning. During the drilling of well VLA-1321, 90’ of samples were taken in the Miocene and 300’ in the Eocene sands with a high percentage of recovery (90.80%) and in well VLA1326, 411’ of samples were cut with a percentage of recovery of 90.4%. Additionally, the electric logs were not affected by the micro-buble mud and caliper logs showed a hole of excellent gage. Judging from the excellent results obtained, the Microbubble Aphron system is still being evaluated in the Eocene mature reservoirs of Lake Maracaibo.