The acid treatment creates conductive flow channels, also known as wormholes, which possess much higher conductivity compared to the reservoir rock. These conductive channels transport reservoir fluids from within the formation matrix directly into the wellbore overcoming both low permeability and near wellbore damage.
In matrix acidizing of carbonate reservoirs, accurate acid placement is a major challenge as the acid tends to flow preferentially toward the highest permeability areas. This can result in overstimulation at these intervals leaving the lower permeability regions untreated. A significant percentage of acid matrix treatments do not meet expectations because of an improper job design. In some cases, after a stimulation job, a huge increase in water production is observed due to preferential stimulation of high permeability sections associated with water.
The Packers Plus RapidMATRIX® multistage stimulation system is a game changing technology that has opened access to several major carbonate reservoirs. In this system, isolated stimulation stages are created by spacing out RapidJET™ nozzles and flanking them with RockSEAL® open hole mechanical packers. The Rapid-JET nozzles are adjusted and placed according to reservoir characteristics enabling controlled injection and leak off for an evenly distributed flow of the acid into the entire section of the interval. The designed treatment is thereby effectively placed at an optimal rate and pressure along the stage length, maximizing the development of wormholes throughout the reservoir zone of interest.
The RapidMATRIX system, alone or in combination with the Packers Plus StackFRAС® system, has been extensively used to exploit the carbonate reservoirs in the oil-bearing Swan Hills area of northern Alberta, Canada and the Khuff gas formation in Saudi Arabia.
An operator working in the Swan Hills area was seeking an effective method to stimulate both the reef and platform sections of the reservoir to increase production. The Swan Hills reefs are well known for their thick stack and excellent porosity and permeability. However, due to the lower porosity and permeability and heterogeneous nature of the extended platform, an advanced completions technology is needed in order to capture the remaining pay in the depleted reefs and exploit the reserves in the tighter platform.
The operator decided to meet this challenge with the Packers Plus RapidMATRIX and StackFRAC systems. For the higher permeability reef complex, the RapidMATRIX system was used to stimulate wells with matrix acidization. For the lower permeability platform, a combination StackFRAC–RapidMATRIX system was used. The lateral lengths of these wells averaged 900 m and had up to 9 stages. The wells that used the StackFRAC–RapidMATRIX combination system had an average lateral length of 1,200 m with up to 14 stages. In both cases, the operator was pleased with the production results and continues to use these systems to exploit the area.
Another example of the successful application of the Packers Plus RapidMATRIX system is in the Khuff formation of Saudi Arabia. The Permian Khuff-C carbonate reservoir is a prolific, non-associated gas and condensate producing member of the giant Khuff reservoir in the Ghawar structure of Saudi Arabia. Extensive heterogeneity in stress, reservoir quality and reservoir fluids throughout the field combined with the deep and hot nature of the reservoir, makes uniform and effective stimulation of all layers a challenging task. In this region, acid stimulation is required either in the form of matrix acidizing or acid fracturing to obtain high production rates and tie-in wells to the production facilities.
A candidate well was chosen to test whether the RapidMATRIX system could increase production. The well was drilled parallel to the maximum horizontal in situ stress. A 3-stage RapidMATRIX system was successfully deployed to total depth in the 405 m lateral. Compared to three offset wells in the region which were completed using conventional coiled tubing matrix acidizing and acid fracturing, the RapidMATRIX completed well produced on average 50% more gas.
These case studies demonstrate the successful application of the Packers Plus RapidMATRIX and combination StackFRAC–RapidMATRIX systems for tight carbonate reservoirs. Advancements in the design of Packers Plus systems provide operators with efficient and cost-effective systems to complete their wells.