Efficient Technology Application to Optimize Deep Gas Well Completions in the Khuff and Jauf Formations Requiring Hydraulic Fracturing in Saudi Arabia

The first phase of an accelerated project to develop Saudi Arabia’s deep gas potential has been sanctioned, and a large number of new gas producers are currently being drilled and completed. A number of wells have been either acid or hydraulically frac’d, and preliminary production tests have shown significant productivity increases resulting from this type of stimulation. Consequently, plans have been finalized to frac most existing and future wells in this development. Fracture initiation pressures average 16,000 psi. at downhole conditions, and H2S has been found present in several of the formations, so well completions capable of withstanding such conditions are of critical importance. This paper describes how the acquisition of WellCat, Landmark’s tubing stress analysis software program, and rigorous scrutiny of well completion components helped Saudi Aramco identify a significant number of mechanical weak links previously overlooked by an in-house computer program. The ability to analyze well completions in intricate detail, and model each frac stage with realistic fluid rheology, provided a powerful tool which helped identify weak links in need of removal to prevent potential problems. A systematic approach to evaluate existing and planned well completions was implemented, close cooperation between several Saudi Aramco groups and Landmark established, specific modification recommendations issued, and an action plan to improve future completions and strengthen existing ones was put in motion. Introduction Saudi Aramco first developed non-associated gas from the Khuff formation in the Shedgum and Uthmaniyah areas of the Ghawar field in the early 1980’s, to provide fuel and feedstock to in-Kingdom industry during periodic shortfalls in associated gas supplies. The ever-increasing energy demand in the Kingdom has turned non-associated gas into an important source of energy. Non-associated gas well potential comes from the Khuff and pre-Khuff reservoirs. A large-scale development program to meet projected high demand and to replace crude burning in some regions of the Kingdom is underway. By 2002, projected non-associated gas demand will be in excess of 3 BSCFD, while current tested well potential is below that rate. A number of programs have been initiated to ensure supply targets are met. These include: exploratory and development drilling, production optimization from existing deep gas wells, debottlenecking of existing gas processing facilities, and design and construction of new facilities. Additional development phases have been sanctioned and implementation will occur throughout coming years. The Khuff formation is a carbonate evaporate. Gas composition varies widely throughout the Ghawar field. The hydrogen sulfide content ranges from 0 to 9-mole %, carbon dioxide from 0.5 to 4-mole %, and nitrogen from 7 to 14-mole %. Average reservoir datum depth is 11,000 ft SS., average initial reservoir pressure 7,500 psig, and average temperature 275 °F. The Jauf formation is a thick sandstone with the presence of fibrous illite clays, which can contribute to formation damage and formation sand production. It produces sweet gas with high condensate content. Average reservoir datum depth is 13,000 ft SS, average reservoir pressure 8,500 psig and average temperature 300°F. The traditional stimulation methods used in existing nonassociated deep gas wells were, until recently, matrix stimulation and perforation acid washing aimed at removing near-wellbore damage. However, the new development areas have shown reduced reservoir quality, which usually renders traditional stimulation methods ineffective. Furthermore, early SPE 68206 Efficient Technology Application to Optimize Deep Gas Well Completions in the Khuff and Jauf Formations Requiring Hydraulic Fracturing in Saudi Arabia J. Ricardo Solares, SPE, Saudi Aramco 2 J. RICARDO SOLARES SPE 68206 testing of a small number of Jauf wells has shown that sand control may be required. A number of acid fracs in Khuff wells and hydraulic propped fracs in Jauf wells have been successfully implemented, thus proving fracturing to be a viable productivity enhancement technique in this development. The significant successes achieved early in the program supported the decision to move forward with a large-scale fracturing campaign covering most of the wells in the development. However, collected field data and experience have shown that hydraulic fracturing will be a challenging and complex task. Measured fracture initiation gradients in the Khuff range from 1.0 to 1.4 psi/ft. Required average treatment pressures for effective fracture growth average 16,000 psi. at reservoir depth, wellhead tubing injection pressures range from 10,000 to 12,000 psi., annular pressures up to 7,000 psi. are needed for tubing support, and treatments are pumped at injection rates up to 80 bpm. Well completions capable of withstanding such harsh conditions are an essential component of the development program. Deep gas well completions in the Ghawar field to date are of two basic types: a) liner top PBR; b) packer top PBR. Both completion types incorporate a seal assembly with allowable upward movement. The majority of wells in the new development phase have been completed with 4-1/2", 51/2", or tapered 15.1# and 13.5# C-95 grade tubing with New Vam connectors. Several L-80 material components were also incorporated in the tubing string. All wells are completed with 7" or 7" x 4-1/2" cemented liners. Cross-sections of typical completions are shown in Fig.1.