Abstract

Generally, after 6 months on production, the rate for the AVA Field wells, producing from the Lower Talang Akar section, declined to 25 BOPD - 400 BOPD. These wells had initial rates in the range of 400 BOPD - 1400 BOPD.

The available integrated rock data shows that the low rate production sandstone reservoirs were deposited in the lacustrine marginal setting and they consist of rich clay minerals, plagioclase and quartz overgrowth. The predominant clay minerals are kaolinite, followed by chlorite, illite and mixed layer illite/smectite. Within the lacustrine sandstone reservoirs, the distribution of the clay in the rock system is very critical. The clay minerals are shown as pore filling and lining, sitting on the surface of the quartz grains or as coating between the grains. These conditions place the clay minerals in the pore space and in contact with fluid. Therefore, they can easily migrate along with the fluid into the pore-throats near the wellbore, resulting in permeability losses near the wellbore.

The higher clay mineral content and higher degree of post depositional compaction effect in the AVA lacustrine reservoirs could be the most important factor causing porosity and permeability reduction within the lacustrine reservoirs. Equally, the sediment transport process may have resulted in better reservoir quality in the deltaic reservoirs than in the lacustrine reservoirs.

Knowledge of the formation damage mechanisms is very important because the wells could be abandoned or shut in if damage is not recognized. In fact, the reserves may not yet have been optimally exploited. Hydraulic fracturing jobs were performed in the AVA Field low producing reservoirs to bypass near wellbore damage and resulted in increasing the oil rate up to 400 BOPD from rates as low as 25 BOPD before shut in.