Abstract
A multidisciplinary well integrity evaluation was performed in Latin America with the objective to improve zonal isolation issues caused by a channel that formed after cement placement between different formations in the production section of the well. The differential pressure between a high-pressure water zone and heavily depleted reservoir was observed to be the main driver behind this issue.
A well integrity service enabled analyzing a large amount of historical data from wells drilled between 2015 and 2016 in a timely fashion. This analysis accounted for a cross-verification of drilling practices, openhole logs, petrophysical evaluations, cement placement, and log evaluations between the wells, which led to formulation of two hypotheses concerning the conditions that are responsible for a post-placement channel:
Differential pressure between water zone (high pressure) and zone of interest (low pressure) was higher than in those cases where crossflow did not happen.
The depleted zone of interest presented higher mobility conditions, which could contribute to making the scenario more prone to crossflow due to pressure leakoff in the sandstone.
Based on these observations and drilling risk analysis, the drilling and completion programs on the subsequent well were adjusted. One of the decisions was to stop drilling before getting into the high-pressure water zone in the production interval. Another one was to optimize the cement placed in front of the high-permeability zone of interest, using high-tier technology with the objective of minimizing the cement-to-formation interactions and achieving enhanced properties.
In the case history, a well drilled with the new drilling program combined with improved cement properties showed adequate isolation across all target formations confirming the success of the well integrity service. Achieving zonal isolation from the beginning allowed the operator to move forward with drilling and completion programs, avoiding nonproductive time and costs that could reach USD 500,000 in remedial operations.
Achieving proper zonal isolation to assure the well integrity requires interaction between the multiple disciplines working in the well construction. By taking the holistic approach provided in the well integrity evaluation service, it was possible increase the level of assurance on cement evaluation interpretation and recognize the main contributing factors for formation crossflow. Mostly important, it provided a new insight, allowing the operator to make better decisions and, together with the service company, define the solution for properly isolating the formations in the production section without the need of remedial operations.
