Nitrogen from Cryogenic Air Separation Process To Be Used for Pressure Maintenance and To Enhance Recovery at Cantarell Complex in Campeche Bay, Mexico
Authors: Kirtley John R. 
Published: October 2008

The Cantarell Complex, located 85 kilometers offshore in Campeche Bay, Mexico, is the major component of Mexico's petroleum asset. Cantarell's primary component, the supergiant Akal Field, has suffered a reservoir pressure decline of over 50% since commencing commercial operations in 1979. A reservoir pressure maintenance study performed in 1996 concluded that injection of high purity nitrogen, at rates of 1200 MMSCFD, provided the optimum means to address the decline in pressure. The project, which included not only cryogenic air separation facilities, but also power generation and gas transmission pipelines, was submitted for bid under a Build-Own-Operate (BOO) contract model in 1997, and was awarded in October of that year to an international consortium of five companies. The successful bidder examined a wide variety of different power generation configurations and air separation process cycles to develop the optimum economics. The final process configuration consists of four Air Separation Unit modules of 300 MMSCFD nitrogen product each. Electrical power is produced by three operating Gas Turbine Generators, outfitted with waste heat recovery via Heat Recovery Steam Generators (HRSGs) with supplemental duct firing. Air compressors are powered by motor drivers, whereas nitrogen product compressors use steam turbine drivers. Plant cooling is based on a closed loop cooling system, which rejects heat to seawater. Product nitrogen is routed 85 kilometers offshore through two 36" diameter pipelines for injection into the crown of the gas cap. Reservoir estimates project an additional recovery of two to three billion barrels of oil relative to continued operations without nitrogen injection and associated upgrades. Anticipated contract life is 15 years. The rated capacity of 1200 MMSCFD makes this the largest nitrogen production facility in the world.

Introduction

Following initial discovery in 1978, commercial production from reservoirs comprising the Cantarell Complex began in 1979. Oil production levels rose rapidly, to one million barrels per day (BPD) in 1981, and Cantarell soon became the mainstay of Mexico's domestic oil program. Production levels averaged nearly 1.1 million BPD in 1996, accounting for approximately 40% of Mexico's entire domestic oil production. Petroleos Mexicanos (PEMEX), through Pemex Exploration and Production (PEP), is by law the owner of all hydrocarbon reserves in Mexico. As such, PEP is also the operator of the Cantarell Complex.

The key asset of the Cantarell Complex is Akal Field, rated as a supergiant and considered to be the sixth largest reservoir in the world. Estimates of the original oil in place (OOIP) suggest approximately 32 billion barrels. Akal is a fractured carbonate reservoir, approximately 30,000 acres in size, located some 85 kilometers (km) offshore from Mexico in the Bay of Campeche. Akal had no original gas cap, and original reservoir bottom hole pressure (BHP) was in excess of 3800 PSIA at the oil column datum. A secondary gas cap formed soon after production was initiated from the field, as the BHP at the top of the structure dropped below the bubble point of 2128 PSIA. Akal Field has a high permeability due to extensive fracturing, a thick (&gt;900 meter) reservoir section, and high structural relief. Those factors, plus the formation of a secondary gas cap, make for an efficient gravity drainage recovery mechanism.