Economic and Technical Feasibility Analysis of the Use of a Water Base Drilling Fluid at Levas Field, Dacion Production Unit, San Tome District Ayacucho Division - Venezuela

摘要

The development of the Levas field began in 1952, by drilling vertical wells using a water-based drilling fluid, however, from 1998 when the aggressive drilling of deviated wells began, also the operational problems started in the middle section, problems such as tight hole, drag, hole instability, stuck pipe, and others. In 2002, the company decided to switch to oil-based mud to reduce and control the incidence of those inconveniences. PDVSA Services San Tome, began searching for a special drilling fluid to replace the existing, due to high demand of the main component of the oil-base drilling fluid (Vassa), and its low supply due, and more important the high cost and environmental difficulties to treat and dispose this kind of drilling fluid and the cuttings. This study evaluated four sets of high performance water-based drilling fluids, to start a new development stage for drilling deviated wells at the Levas Field. To determinate the technical feasibility, some studies were made, first the physical properties, such as: rheology, filtration, solids percentage in the system, and others, were evaluated to make a comparative analysis to find out which water-base drilling fluid had the best performance considering the geological and operational conditions of the field. Also the mineralogy (clay minerals) of the field was determinate through the X-ray diffraction test, which concluded that the predominant mineral of the field was kaolinite. This clay has a low CEC value that means it has a high dispersion capacity. This result allowed to determinate one of causes of the hole instability in the middle section of the deviate wells. Additionally, the Dynamic Linear Swell test was made to determinate the inhibitory capacity of each water-base drilling systems with the clays from the formation and bentonite, beside the clay dispersion test evaluated evaluate the capacity of each high performance drilling fluid systems to maintain the integrity of the body shale and cuttings. Finally, the cost analysis allowed evaluating the economic feasibility of each drilling fluid system. After analyzed the various results, we concluded that the drilling fluid trading system number one had the best cost benefit to drill deviated wells in Levas Field.