Water imbibition studies were conducted on core plugs at confining pressures of 2,000 psi. Water was enriched with CO2 at different carbonation pressures, ranging from 50 to 500 psi. Conventional displacement as well as Nuclear Magnetic Resonance (NMR) methods were used to study the effects of carbonated water imbibition on oil recovery rate and ultimate recovery. The major factors influencing Oil recovery by carbonated water imbibition displacement appear to be:An increase in oil mobility. An increase m core permeability in carbonate cores A reduction in the operating pressure below the bubble point pressureafter the core had been allowed to imbibe the carbonated water induced asolution gas drive effect which substantially increased recovery. Carbon dioxide dissolved into the water being imbibed by the rock was found to accelerate oil recovery rates and increase ultimate oil recovery when compared to unadulterated water imbibition. Recovery rate and ultimate recovery increased as a function of the amount of CO2 dissolved into the imbibed water. Recovery time was reduced to one third when the gas liberation process was applied cyclically. This new method holds promise to increase oil production rates and oil reserves from fractured, low matrix permeability, low gas-oil ratio, oil reservoirs. II. Introduction Naturally fractured, dual porosity oil reservoirs present a particular oil production problem. Usually oil is readily produced from the fracture portion of the system. However, the oil located in the, matrix blocks is not easily displaced because of the relative ease of the fluids to channel through the fractures and bypass the matrix pore system. The application of any external drivemechanism to displace oil will mainly affect the high permeability avenues of the fracture system. Generally, the matrix blocks remain essentially unaffected by normal secondary enhanced oil recovery oil displacement methods. Figure 1 illustrates the flow problem for this particular type of reservoir. The effects of capillary forces to spontaneously imbibe water into the matrix blocks has previously been used to displace otherwise unrecoverable oil reserves. Several tests on the Spraberrry field, and other fractured reservoirs have proven that spontaneous water imbibition can be an important oil producing mechanism. However, the process with counter current oil flow is usually very time dependent. The inclusion of CO2 in the imbibed water could not only possibly accelerate but also increase oil recovery from the low permeability matrix blocks in a fractured, dual permeability reservoir. The use of CO2 as a method to increase oil recovery has been previously studied. The most important mechanisms leading to higher oil recovery are:CO2 becomes miscible with water and most crude oils at pressures greater than 1,400 psi,CO2 might create swelling of oil,CO2 has an acidic effect on calcareous rocks, andCO2 creates a gas drive when pressure depleted below carbonation pressures. However, no one has studied the effect of replacing unadulterated water with carbonated water to accelerate and increase ultimate recovery by the water imbibition-oil displacement process. This idea would be very applicable to enhancing oil recovery from dual porosity, naturally fractured, carbonate oil reservoirs. P. 79^
Saudi Aramco experienced serious corrosion problems in oil production tubing in one offshore field, attributed to presence of H2S, CO2 and varying levels of water cut. In early 2002, the company installed on trial test basis Glass Reinforced Epoxy (GRE) or commonly known as fiberglass lined carbon steel tubing in three wells. The fiberglass lining was installed to provide a corrosion barrier to protect the steel tubing from internal corrosion. As far the technology, the fiberglass lining or sleeve is carried out joint by joint by inserting a solid fiberglass tube into the low cost carbon steel tubing and cement is pumped into the narrow annulus between the fiberglass liner and the carbon steel tubing. The connection area is protected by the combination of end flares and a corrosion barrier ring. The company examined various methods to evaluate the performance of the fiberglass lined tubing, without having to pull out the tubing from the well as these wells are oil producers. After review of the evaluation options, it was decided to run a multi finger caliper to evaluate the condition of the fiberglass lining and check for any internal corrosion in the steel tubing. The log showed the fiberglass lining to be in good condition with no damage indicating that the steel tubing was protected from corrosion. The other two wells had no tubing leaks indicating the GRE lining is providing corrosion protection. Based on successful trial test results, the company adopted the technology to protect tubing strings deployed in corrosive environments in oil producers, water injectors and water supply wells. Field experience has shown that the use of fiberglass lined tubing is a low "life cycle cost" solution compared to other options. There has been no workover in these wells since installation. Today fiberglass lined tubing is applied in Saudi Aramco in high water cut oil producers, water injectors and combined water source and injection wells. The paper shares the history of corrosion, challenges and lessons learned during the implementation of the solution, various performance assessment methods evaluated and the results and interpretation of the caliper log.
Casing-while-drilling is a relatively new well construction process or technology for simultaneously drilling and casing a wellbore, and has been utilized globally over the last 15 years or so. This technology has shown advantages of reducing overall drilling time and cost. It has demonstrated signs of reducing hole problems, such as mud losses, through plastering effect because of the rotation of the casing string against the formation. It provides assurance to case off unstable formations while drilling, resulting in significantly reduced well construction costs. Saudi Aramco has made several field test runs of this technology beginning in early October 2008, including deployments of both simple casing drilling with drill-through casing bit (non-retrievable) system and advanced bottom hole assembly (BHA) retrievable system designed for directional casing drilling. This paper will document the lessons learned from implementation of the technology, including planning and design, rig operations, problems encountered, modifications made to reduce risk after extensive review and investigation, and finally, successful deployment of a directional casing drilling to the planned casing point with a 17" x 13-⅜" system. In addition, the paper briefly outlines the further required improvements of casing drilling tools to ensure continued success in the future.
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