Design of a Fracturing Fluid for a Deepwater Well
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 103089, "Systematic Approach to the Design and Application of a Well Fracturing Fluid To Ensure Deepwater Production," by E. Park, SPE, and K.E. Olson, SPE, BP America, and B.J. Weber, SPE, K.E. Cawiezel, SPE, T.D. Monroe, SPE, C.S. DeVine, SPE, J.L. Cutler, SPE, and S.L. Berry, SPE, BJ Services Co., prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24-27 September.
Fracturing fluids are presented with unique challenges in well depths that can exceed 20,000 ft with pore pressures greater than 20,000 psi. One major issue facing deepwater fracturing is generating sufficient bottomhole treating pressure to create a hydraulic fracture at the sandface without exceeding the limitations of the hydraulic equipment at the surface. The full-length paper summarizes a study to design, test, and qualify a sodium bromide (NaBr) weighted, delayed-crosslink fracturing-fluid system for use in deepwater fracturing.

Introduction
The number of oil and gas exploration projects in the deepwater areas of the Gulf of Mexico (GOM) and other offshore locations has increased in the last decade. However, along with the economic rewards of producing these giant fields comes a set of difficult operational challenges. Development activities in all areas of drilling, completion, and production of these wells have faced significant challenges as a result of the combination of high bottomhole pressures and temperatures (BHTs). To reduce the uncertainties in these areas, experienced teams of key personnel were formed in their expertise areas to address development of new systems and to enhance preplanning activities, risk management, and quality-control procedures in all areas of the completion processes.
One key area of concern in the completion of these deepwater wells is the design, application, and compatibility of the fracturing fluid to obtain maximum well production. One of the major issues facing deepwater fracturing is generation of sufficient bottomhole treating pressure to create a hydraulic fracture at the sandface without exceeding the limitations of the hydraulic equipment at the surface. To overcome these surface hydraulic-equipment limitations and still create the required hydraulic-fracturing pressure at the sandface, weighted fracturing-fluid formulations have been developed. Because of the increased travel distance to the sandface and the extreme temperature ranges to which the fluid is exposed from the mudline to the BHT, the fracturing fluid must be designed to meet extended crosslink delay times and specific density, frictional-pressure-loss, and compatibility specifications.
This deepwater-project study was based on water depths as great as 6,000 ft and wells at least 25,000 ft deep. As a result, the anticipated surface and bottomhole treating pressures could be the highest ever required in the GOM.

Fluid Rheology Requirements
Calculated surface pressures necessary for hydraulic fracture at the sandface and not exceeding the limitations of the hydraulic equipment at the surface showed that a weighted, delayed-cross-link fracturing-fluid system would be the fluid system of choice. Rheological-performance requirements for the frac-pack fluid as outlined by the operator call for a fluid system with a viscosity greater than 400 cp at 170 sec−1 for 60 minutes, and breaking to less than 50 cp in 90 minutes at a 200°F BHT.