Investigation of Natural Gas Hydrates in Various Drilling Fluids

Abstract

SPE Members Abstract This paper presents laboratory-derived equilibrium temperature and pressure data for gas hydrates in drilling fluids. Data are included for lime sea-water gypt polymer and dispersed muds with varying salt polymer and dispersed muds with varying salt concentrations, as well as several experimental fluids. Equilibrium curves to determine salt requirements in deep-water drilling muds also are included. Introduction Gas hydrates can obstruct deep-water well-control operations. Baker and Gomezi recently published two case histories in which gas hydrates plugged subsea risers, BOPs, and choke and kill lines during well-control operations. The first well was drilled in 1150 ft (351 m) of water with a sea-floor temperature of 45 OF (7.2deg. C). Cementing operations were required to secure the well after hydrate plugging prevented the use of either choke or kill line. In the second well, the choke and. kill lines became plugged several days after the well was initially shut in. Hydrates also prevented the BOPs from operating properly. prevented the BOPs from operating properly. Multiple kill operations were required to eventually control the well. Water depth was 3100 ft (945 m) and the sea-bed temperature was 40deg. F (4.4deg.C). Gas hydrates, ice-like crystalline solids formed by the physical reaction of gas and water, can form in aqueous systems at temperatures well above the freezing point of water if the pressure is sufficiently high. According to Churgin and Halminski, the average sea water temperature in the Gulf of Mexico decreases rapidly to 48 deg.F (4.4deg.C) by 300 ft (914m) as shown in Fig. 1. Low temperatures, when coupled with the pressures encountered during well-control operationist, create an environment conducive to the formation of gas hydrates. Furthermore, the liberation of large quantities of gas near the surface during hydrate decomposition may create a dangerous well-control situation. Despite the potential hazards, little data have been published on gas-hydrate formation in drilling muds. One reason is the lack of equipment available for mud studies. The first part of this paper is the description a dual-cell gas-hydrate generator recently developed at M-I Drilling Fluids Engineering Research Laboratory. The remainder of the paper is a discussion of data obtained using this device on various common and experimental drilling fluids. The data can be used to help formulate a water-base drilling mud to achieve a desired level of hydrate inhibition. GAS-HYDRATE GENERATOR Gas hydrates can be formed in the laboratory by reacting gas with water-base drilling fluids in a pressure cell exposed to temperatures in the vicinity of the freezing point of water. point of water. P. 181