Erosion Mitigation During Testing of High Deliverability Gas Well - A Case Study

Abstract

Abstract The paper details the case history of a highly challenging, high deliverability exploratory gas well that was successfully drilled and completed in the frontier region. The 4,900 m well encountered multiple reservoirs during drilling with severe losses in the topmost prospective limestone reservoir formation. Subsequently, well was cased and Drill Stem Test (DST) was performed to test reservoir deliverability. During testing, severe leakages were encountered at the Surface Well Test (SWT) equipment due to high flow velocities, coupled with Loss Control Material (LCM) and formation cuttings flowback. This led to internal erosion in the equipment, resulting in frequent uncontrolled hydrocarbon release into the atmosphere, posing a high risk for personnel. Consequently, frequent shut-ins for maintenance were necessary. Steps taken to mitigate this issue are discussed and recommendations are proposed for future encounters. A systematic approach was adopted to offset the effects of erosion and consequential leakages. Points were identified which were prone to leakages, and successively, steps were taken to minimize bends. Non-intrusive thickness monitoring was carried out regularly to detect reduction(s) in the pipe schedule preemptively and take appropriate measures. Erosional velocities were computed for different pipe sections and sufficient back pressure was applied to reduce flow velocity. Other measures such as reducing flowing times at higher chokes and acid stimulation were also carried out to minimize the impact of, and dissolve, the particles eroding the equipment. Significant improvements were observed after taking preventive measures – Non-Productive Time (NPT) was reduced, and the remaining job was carried out safely without any impact on the personnel, equipment, environment and the Company reputation. Accuracy of the collected data also improved, as particles had inadvertent effects on flow measurements. An extensive study was carried out followed by on site actions to reduce the erosional impacts on a high pressure, high deliverability gas well. Important conclusions were drawn. Safe practices were developed to avoid future occurrences in high volume wells. A combination of steps such as re-arrangement of SWT setup to minimize bends, monitoring pipeline thickness using ultrasonic thickness meter, minimizing flow duration at high chokes, calculating downstream pressures required to limit erosion and applying back pressure, and performing acid stimulation can all help future operations to be carried out safely without any untoward downtime. In addition, dissolvable / degradable LCM could be opted in future wells, and wellbore hydraulics could be further studied to ensure optimum hole cleaning for effective cuttings removal.