Case Studies Validate the Effectiveness of Aluminum-based HPWBM in Stabilizing Micro-Fractured Shale Formations: Field Experience in the Peruvian Amazon

Abstract

One of the most important functions of drilling fluids is to maintain adequate wellbore stability until casing is run and cemented properly. Lack of wellbore stability generates an enlarged non-homogeneous elliptical weaker borehole. This non-cylindrical shape of the wellbore leads to complex drilling problems such as poor hole cleaning, high solids production, stuck pipe, unsuccessful wireline runs, poor cement bond representing large cost to operators. Micro-fractured shale formation represents a challenge due to its natural lack of stability when exposed to conventional water-based mud (WBM). As a solution, oil-based mud (OBM) becomes a technical option to overcome the issues observed with conventional WBM. It tremendously reduces the chemical interaction with micro-fractured shales. However, environmental constraints of the OBM makes this option non-applicable for environmentally sensitive areas. According to recent publications, with similar complicated environments, Aluminum-Based High-Performance Water-Based mud (HPWBM) has shown good performance with features closely comparable to that of OBM. The Peruvian Amazon has the largest Peruvian oil and gas reserves. However, it is located in an environmentally sensitive area marked by a large biodiversity and native communities. Environmental concerns related to drilling activity are very restrictive. Furthermore, most operations are performed as “offshore on land” (i.e., helicopter-transportable operation) where drilling fluid management cost strongly affects the final Well’s Authorization for Expenditure (AFE). Aluminum-based HPWBM has been successfully introduced recently in the Peruvian Amazon for drilling vertical and deviated wells resulting in considerable improvement in drilling performance and goal achievements. Issues related to shale instability were previously reported and financial losses forced operators to use Aluminum-Based HPWBM to reduce non-productive time and associated costs. Two groups of case studies from four wells drilled in Blocks 8, 56 and 88 blocks of the Peruvian jungle are presented in this paper. A Wellbore Quality Index (WQI) tool and Key Performance Indicators (KPI) are introduced to make comparison between aluminum-based HPWBM and previously used (i.e. conventional) fluid systems and to validate the effectiveness of the aluminum-based HPWBM system in stabilizing micro-fractured shale formations. A proper fluid design was selected during the planning phase of each project and fluid properties were monitored at the rig site to evaluate performance. In addition, wireline logging, casing runs, trips, wellbore quality and drilling performance were closely monitored to examine the impact of using aluminum-based HPWBM. Results show tremendous performance improvement introducing a new benchmark in drilling operation in the Peruvian Amazon.