In the moderate-permeability environment of the Hassi Messaoud field of central Algeria, proppant fracturing has significantly increased production, prolonging the economic life of many wells. Unfortunately, the logistics of mobilizing a workover rig to prepare the wellbore for stimulation has extended the stimulation cycle time. Additionally, many wells have tubular problems that require intervention such as squeeze cementing or tubular replacement before the stimulation process can begin. The availability of coiled-tubing equipment in the field provides the means to stimulate the wells without a workover rig. Furthermore, when coupled with a mechanical isolation system, the coiled-tubing fracturing technique protects the production tubing from high treating pressure and abrasive proppants. In the past, the lack of a reliable isolation system has limited the success of these jobs.
Reservoir conditions throughout the field allow low-rate stimulations but induce high bottomhole pressures, which make the use of conventional packers difficult. In many environments the bottomhole treating pressure creates differential pressures across the elements of a packer in excess of 9,000 psi. Several attempts to use existing packer technology yielded unsuccessful fracture treatments, and costly fishing operations were necessary to restore the wells to production. To provide an economical solution to the problems encountered by conventional mechanical packers, a new isolation system was designed. This paper provides case histories of several wells stimulated with coiled-tubing fracturing in the extreme environment of high-pressure, deep wells in the Hassi Messaoud field and examines the engineering challenges in developing a robust isolation system.