Formation Fracture Gradient Enhancement by Wellbore Strengthening Strategy in Tunu Mahakam Field

Abstract

Through the lifetime of a mature development field, depleted formation pressure could be a challenge in drilling operation. Cases of loss circulation occurred due to induced fracture which is caused by lower formation fracture gradient that will lead to a huge cost impact and operation complexity. The well known technique of "wellbore strengthening" (WBS) is one of an effective solution which can be implemented in the field of Pertamina Hulu Mahakam in Mahakam area East Kalimantan.
This technique is an integrated engineering solution which starts from gathering the geomechanics data of the typical formation, and then simulated the possibility of the fracture opening due to the high ECD versus weak formation pressure by using computer aided software. Furthermore, the raw data of the width fractured will be analyzed to be compensated with the design of bridging material which will be used in drilling fluid. Bridging material used in this project is metamorphic CaCO3, which has a special feature as high compressive strength material and an acid soluble material. The combination of different size of bridging material is used for an optimum bridging effect. Based on the computer aided software result, the combination of the CaCO, size as well as the variety in concentration is tested in the lab to prove the sealing efficiency. The software also suggested the concentration of the bridging material to be used in dependency of the fracture width possibility.
The engineered solution has been successfully implemented in two wells, which has been proven that the strength of the formation is gained post treatment with the WBS strategy. There were no losses during drilling phases as well as during cementing operation. The success of this project implementation will open the opportunity to have a lighter well architecture design, which also means to have less expenses per well drilled.