Publications

We will demonstrate a closed-loop approach to improve the understanding of the hydraulic fracturing process that was applied by Pertamina EP in the Tanjung field. The Tanjung field produces from low-permeability Lower Tanjung conglomerate formation and generally requires hydraulic fracturing for economical production. However, proper geomechanical modeling was required to understand fracture growth and its impact on production. Based on fracturing experience in the area, in the lower zones, it was believed that the fractures could have the possibility of uncontrolled height growth and limited propped fracture length. A fracture condition such as this could exist due to the considerable thickness of the reservoir and the absence of any effective stress barrier. This assumption was based on surface pressure analysis obtained during previous fracture treatments and actual data were needed for confirmation. A better understanding of fracturing performance can also help improve the formula design, leading to better production. Pertamina EP and Schlumberger identified the need to reduce fracture growth uncertainties by use of geomechanical modeling and monitoring the fracture growth. This goal was accomplished in the following steps. Initially, detailed data acquisition, including the latest acoustic anisotropy logging was planned and executed in the target well to aid in constructing the mechanical earth model (MEM) which is a numerical representation and understanding of the local stress regime and stress barriers that could hinder fracture growth. Advanced interpretation and processing of waveforms provided local stress directions, earth stress magnitudes, and mechanical properties of the rock, which were then incorporated into the fracturing design. Thus, the fracturing in each zone was designed according to its properties provided by the MEM numerical representation, which was a different method than the previous fracturing work in which the zone properties were estimated based on assumptions from simple logs like Gamma Ray. Provisions for better estimates of the stress and rock strength obtained from the MEM modeling reduced significantly the uncertainty in fracturing design. In the second step, prior to the main fracturing operation, a minifrac was performed to obtain the formation parameters. The results of the minifrac were used to calibrate the MEM model, which was then input into the fracturing design. In the third step, after the main frac was conducted, the acoustic anisotropy tool was again run in the cased hole. A comparison of the cased hole acoustic anisotropy log with openhole data identified the fracture height near the wellbore. Excellent and repeatable signal quality also helped identify intervals that were better propped than others. The analysis confirmed that due to absence of effective stress barriers within the reservoir, the fracture grows in height near the wellbore with limited fracture half-length, leading to a better understanding of fracture geometry and effectiveness.