Abstract

In recent years, there has been an increase in exploration and drilling activity in deepwater and deep-shelf gas and oil fields in the Gulf of Mexico. The economic feasibility is dependent on completion efficiency, with the goal to optimize the production rate.In addition, most of these formations require sand control to prevent completion failure.To achieve optimum hydrocarbon production and prevent sand failure, frac-pack is considered the best completion option. However, performing frac-packs in deep reservoirs (>15,000 ft) with high reservoir pressures (>10,000 psi), and temperature variations pose many challenges such as pump rate limitations due to high friction pressure and fluid-stability problems due to temperature changes.

To address these challenges and overcome the limitations of conventional fluids, a unique borate crosslinked that employs an encapsulated borate crosslinker with various base-fluid compositions was developed.

  • The fluid has a broad temperature stability range: 40°- 350°F.

  • The crosslink-delay can be varied between 1–20 minutes without affecting fluid stability.

  • The proppant-transport ability is excellent.

These attributes allow fluid injection at optimum rates with minimum friction pressure.This paper presents Gulf of Mexico, deepwater case histories that demonstrate the successful application of this fluid. The fluid design, fluid properties, and job execution, are discussed in the paper context.

Introduction

The Gulf of Mexico (GoM) produces approximately 1.6 MMBOPD - about 25% of US oil production.The GoM is divided into to principal areas: shelf (water depth > 1,000 ft) and deepwater (water depth > 1,000 ft).

Until 1995, shelf reservoirs were the predominant contributors to production. However, discovery of prolific reservoirs in deepwater shifted production and currently 61% of production comes from deepwater reservoirs.[1] Earlier deepwater reservoirs were shallower (>10,000 ft TVD) and intervals lengths were smaller (>100 ft).As these shallow reservoirs were being depleted, exploration and development began in deeper reservoirs with large interval lengths.Currently, it is not unusual to complete reservoirs deeper than 25,000 ft TVD.

The shallower reservoirs did not require executing frac pack treatments at rates over 20 bpm. However, deeper reservoirs require higher pumping rates. For example, in 1999, a deepwater well (18,700 ft MD and 18,200 TVD) in the Mississippi Canyon had an interval length in excess of 270 ft MD and 170 ft TVD.In order to obtain an optimum frac pack, pumping rates of 40 bpm were required to execute the job. This was a drastic step for the industry in terms of horsepower, hardware capabilities (packer and service tool components), and treating pressures limitations. Since then several deepwater completions have been performed at even greater reservoirs and water depths.These completions continue to bring challenges in terms of surface treating pressures that currently are limited to 15,000 psi by wellhead, tools and equipment ratings.Also, the fluid undergoes high frictional pressures and temperature changes. Mud level temperatures are often lower than 40 OF (mud line temp), while reservoir temperatures are relatively high (>250O F).

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