Abstract

This paper briefly describes a process developed to reduce drilling risks and well costs and gives details on its application to three deviated development wells in Camisea, Peru. Previous offset vertical and deviated wells in this area encountered wellbore instability, drilling fluid loss, and reactive shales. In some cases these events made it necessary to drill multiple sidetrack wells.

The process provided specific advantages while drilling technically difficult trajectories. Integral to the process was development of a mechanical earth model (MEM) for prediction of drilling events and down hole drilling risk management. The model, created using data from multiple disciplines (seismic, drilling, geology, wireline logs, core testing), enabled the drilling team to understand potential drilling hazards and quickly act to mitigate risks, as well as to make rapid informed decisions while drilling. Examples demonstrate how the process compared forward predictions with actual results and how the model was updated during drilling.

The first well reached total depth (TD) 5 days ahead of schedule even though the trajectory was in a difficult stress azimuth and several nondrilling problems occurred. Teamwork and communication among the drilling location and four offsite offices played a critical role in the decision process. Predrill predictions matched post-drill information in most cases. Lessons learned from the first well were applied to subsequent well plans.

This process can be applied to any exploratory or development well, but high-risk, high-cost wells receive maximum benefit. Although wellbore instability resulting from tectonic stress was the main risk in this field, the process is equally valid for drilling issues such as overpressured regimes, underbalanced drilling or extended-reach wellbores.

Introduction

The Camisea blocks (38/42) are located in the tectonic active foothills of the Peruvian Andes (Fig. 1). Initial discovery of the San Martin structures and drilling of exploratory wells occurred in the mid 1980s and early 1990s. Wellbore instability, drilling fluid loss, and reactive shales were common drilling problems and in some wells made it necessary to drill multiple sidetracks.

In this remote jungle area, environmental issues and logistics constrain multiple pad locations for development wells. Drilling of multiple deviated wells is done from a single pad, similar to offshore platform drilling. Early in the planning, it was realized that directional wells would be more costly and incur additional risks. To evaluate the potential risk and plan for mitigation, a core team was designated to analyze previous drilling problems, create a plan for reduced risk drilling, and monitor and update the plan while drilling. The team consisted of experts in geomechanics, drilling, geology, petrophysics, and seismic from the operator and service companies.

As members of the team were geographically separated, a real-time monitoring system (Fig. 2) was used to keep everyone informed and to disseminate information. This system allowed secure posting of reports and documents to share with other team members along with real-time monitoring of rig parameters and downhole sensors via the Internet.

To show how the process worked, we begin by covering the initial planning for the first well, describing how the plan was applied and updated, then examining results from three wells.

Developing the Process

Drilling in technically demanding areas brings associated risk of the unknown. Without a geomechanics model constructed, small problems can become costly. Decisions are often made less on fact and more on feel. Building a geomechanics model after a problem occurs in real time is not a realistic solution given the short time frame needed for most drilling decisions. Having a plan and geomechanics model in place enables personnel to focus on signals before drilling events become a serious problem. When problems do occur, a model allows rapid, informed decisions to be made by the drilling team.

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