Analysis and Phase Behavior of Khuff Gas System in Bahrain Field

Abstract

Abstract Khuff gas is the most important resource in Bahrain. About 90% of Bahrain's total energy needs, including power generation either for public utility or for industry, depends on the Khuff gas. In addition, it is used currently as a feed-stock to the petrochemical and refining industries, and for injection and artificial lift in the Bahrain oil field. A good knowledge of the phase behavior of the Khuff system is important to predict reservoir performance and future processing needs. This performance and future processing needs. This knowledge is also necessary to study multiple contact, partially miscible oil recovery projects in the partially miscible oil recovery projects in the Bahrain oil field which involve injection of the Khuff gas into the Mauddud and the Arab reservoirs. In 1985, the Bahrain National Oil Company (BANOCO) launched a program to sample and analyze the Khuff gas. The objective of this program was to determine any lateral or vertical variation in Khuff fluid composition (Khuff formation covers 66,000 acres and consists of 2100 ft. thick dolomitic carbonate), to conduct laboratory experiments that are required for studying the phase behavior, and using the laboratory data to construct a mathematical model of the Khuff system based on the Peng-Robinson Equation of State. Khuff gas wells 311, 359, 361, 369 and 372 were selected for sampling to provide optimum areal and vertical coverage of the three main Khuff intervals KO, KI and KII. Prior to sampling, the wells were conditioned by flowing at a flow rate of ±25% of the AOF potential during an extended period of time. This relatively low production period of time. This relatively low production rate was maintained to avoid any liquid drop-out in the formation which would lean out the samples. The sampled wells were flowed through a three phase separator at an average pressure of 1000 psig, in which gas and liquid rates were measured every hour to verify that the production rate remained stable during the test. The standard sampling procedure was to fill the liquid sample cylinders to full separator pressure and the gas sample cylinders to 60 – 75% of the separator pressure to prevent condensation in the sample container. The separator gas sampling manifold was provided with a side line to measure on-site the H2S and CO2 contents of the Khuff gas by using Kitagawa stain tubes. The sample cylinder pressure and temperature were recorded for all liquid and gas samples. The opening pressure of the sample cylinders were measured at the laboratory to verify that no leakage had occurred in transit.