A Novel Approach for Stimulation of Heterogeneous Thin Layered Reservoir in an Offshore Field, Abu Dhabi

Abstract

The current practice of stimulating thin layered carbonate reservoir using conventional acid stimulation techniques (CT stimulation or Bull-heading with CDC) have proven to be ineffective and inefficient as acid tends to propagate more in the higher permeable streaks than low permeable ones. The new approach aims at addressing this problem by increasing the contact surface in the lower permeable streaks to improve its productivity using expanding metal needles. The vendor has developed a new method for acid stimulation of carbonate reservoirs. The system is encompassed in self-contained subs which are integrated in the open-hole liner and placed opposite to zones of interest. Acid is bullheaded and a large number of small diameter tubes (needles) jet out simultaneously from the wellbore to penetrate the reservoir, creating numerous flow tunnels. The major application for this technology is to enhance well productivity by connecting the wellbore to the body of the reservoir with as many as 300 flow tunnels. These tunnels drain increase the surface area of the low permeability reservoir layers exposed to flow and hence increase well productivity and reserve recovery. After completing the stimulation job, a special tool is run to clear the open-hole liner from the metal tubes and keep production ports open to allow accessibility to reservoir for injection or production as well as running of production logging tools for reservoir monitoring. The new system (4-1/2″) was successfully installed in one well but cleaning of open-hole liner failed due to design problem related to the cleaning tool. Several meetings with vendors have resulted in a wealth of lessons learned on how to improve the system for future application. As such the well is capable to flow but accessibility for intervention is limited. The initial unloading of the well showed encouraging results from the Fishbone stimulation however later the analysis of flow test monitoring with bottom hole pressure showed decrease in productivity by 35% within short diction of time (~ 2 months). This type of performance has not been seen in other open hole horizontal wells in the field. Also the GOR of the well has increasing trend from the beginning of the production, possibly due to developed communication with top high GOR layer.

A Novel Approach by Needles in the Payzone of Heterogeneous Tight Carbonate: A Case Study for Offshore Marginal Field

“…The initial plan for this heterogeneous tight reservoir is a multistage acid fracture, significantly improving productivity without complicating drilling and well completion [2][3][4]. As normal acid frac job and up to 10 MSF stages were assessed, the result shows us that the stable production period did not increase much after the number of stages exceeded 7.…”