Much has been written about revitalizing mature oilfields. Everyone gets lucky now and then by finding a bypassed oil zone that has not been perforated and as a result sizeable oil production is obtained. The production from these zones, however, is often short-lived due to the limited pay.

The high-level and seasoned consultants of A&A Consulting Team have worked for many years extracting the last economic barrel from mature/marginal oilfields, and can quickly identify if the field has good potential or not. A&A consultants have also developed some unconventional techniques that may extend the life of the field considerably. These methods can be characterized as: (1) plug down and run pulsed neutron or carbon/oxygen logs to look for bypassed oil, (2) maximize fluid recovery through use of gas lift or submersible pumps so that economic production can be achieved by maximizing fluid production, and (3) inject water to raise reservoir pressure and alter the streamlines of production to recover bypassed oil. 

Many wells were plugged back in the 1950s and 1960s, when oil prices were low, yet the well was still producing at good oil rates based upon today's standards. Many operators were also blindfolded by their mode of production (flowing, rod pumping, or gas lifting), and could not consider producing the reservoir at higher withdrawal rates due to the high upfront capital investment required. An operator would also never consider injection of water into a moderately strong waterdrive reservoir to alter the streamlines to flow so that higher oil recovery could be established. At today's oil prices, some of these alternatives are attractive.

The first step to identify the potential of a mature/marginal oil field is to compile good well histories with perforations and production records for each zone. A 20 BOPD producer back in the 1950s or 1960s was unattractive when considering zones further up the hole, but these zones can now provide substantial cashflow. Many wells were plugged back during the early years due to higher anticipated oil and gas production rates from zones above. This resulted in many barrels of bypassed oil, which can now be recovered at these higher oil prices.

The economic conditions of the 1950s and 1960s also often prevented the installation of large gas lift systems or submersible pumps in small fields. This limited the fluid withdrawal rates and reduced the oil percentage, which could be considered economic. By running sand control (if required), and producing the wells at higher rates today, increased oil reserves can be achieved.

While not an obvious method to increase oil recovery from mature oilfields with strong waterdrive, the injection of water into selected wells can alter the flow regimes (streamlines) in the reservoir. A&A consultants have seen this first hand where a strong waterdrive reservoir was subjected to water injection prior to CO₂ injection and higher oil recovery was achieved. The water injection not only raised reservoir pressure, which increased well productivity, but also pushed bypassed oil (due to well spacing) to the producers. The high productivity index of the wells allowed for increased production as reservoir pressure increased, and the water injection pushed oil away from the faults and unswept areas of the reservoir to increase oil production.

The high-level and seasoned consultants of A&A Consulting Team have extensive experience in revitalizing mature/marginal oil fields, and will be delighted to assist you in maximizing oil production rates and reserves from your company’s mature/marginal oil fields.