Frac Packs - State of the Art
Authors: Tiner Robert L. , Ely John W. , Schraufnagel Richard 
Published: December 2007

Over the past four years, there has been an increasing amount of success with fracture stimulation of unconsolidated Miocene formations. These "frac pack treatments" are typically used to remove near well damage produced during drilling operations and also to allow a tremendous amount of surface area for production rather than producing through perforation tunnels. A thorough study of the technology used in frac pack stimulation as well as all types of gravel pack/frac pack treatments has been conducted to define the state-of-the-art. Major operating companies in the Gulf of Mexico were contacted and a very large data base indicating the growing success in utilization of frac pack versus conventional gravel pack or high rate water pack completions was assembled.

The vast majority of the frac pack treatments are presently being conducted through gravel pack screens. These fracture treatments are typically conducted in the circulating position allowing real time diagnostics for fracture stimulation. New rigless frac pack and screenless frac pack completions are the growing trend. This systematic study shows the trends of both the major oil companies and independent companies within the Gulf of Mexico.

Introduction

Over the past year, a fairly comprehensive study has been conducted evaluating all phases of "frac pack" stimulation procedures in the Gulf of Mexico. Included in the study were not only numbers and types of treatments but also the companies particular approach as well as their perceived needs and requirements for equipment and research.

Fracture treatments have been utilized for over 45 years to improve the production rate from oil and gas wells. The early treatments were utilized to remove the effects of damage near the perforations. The early successful treatments were usually small and were performed on reservoirs which were high enough in permeability to produce economically in a non-damaged state. Stimulation, defined as obtaining a negative skin, could not be attained on these wells with the available fracturing technology. A great deal of research in the area of fluids, proppants, equipment, treatment design, and theory has taken place since 1949 when the first commercial treatments were performed. The emphasis over time has switched to fracture stimulation of low permeability reservoirs where negative skins were necessary for the economic development of the reservoir. While fracturing treatments were still an accepted means to remove damage in high permeability reservoirs, acidizing was definitely the process of choice for several years.

Many of these high permeability reservoirs are also plagued with sand production problems due to their poor consolidation. Wells in these reservoirs have typically been completed using gravel packs to eliminate the sand production. Gravel packs inherently create a damage situation and thus lower the potential production in most instances. One major production company has estimated that over 50% of their production capability is lost through gravel pack completions. A positive skin of +5 to +10 is considered excellent using this procedure but skins of +40 and higher are reported.

High rate water pack techniques have been utilized to reduce the damage effect by placing proppant outside the perforation. However, this technique is limited in its ability to eliminate the effect of reservoir damage beyond the wellbore It's advantage over typical gravel pack operations is probably due to reduced skin within the perforation tunnel. Skins of about +2 to +5 are the reported norm for this process.

More recently, developments in fracturing technology and the recognition that results using this technology to fracture through damage are often superior to gravel packing and sandstone acidizing have lead to widespread use of frac pack treatments. This technique has also met with success in controlling sand production from poorly consolidated formations. The skin reported is normally 0 to +2 with a few reports of negative 0 to -3 skins. Most operators who performed post-frac build-ups reported a skin decrease over time when the frac pack procedure was utilized while high rate water packs and gravel packs showed an increase in skin over time.

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