Offshore exploration in Kuwait commenced in 1961 with the award of a 5,600 square kilometre offshore concession to Shell. Some 6,300 kilometres of 3-fold analogue seismic were acquired in 1961, and 3 wells were drilled during 1962 and 1963. In the same period, Kuwait Oil Company (KOC) also drilled their first 3 offshore exploration wells. In 1981, KOC embarked upon a second offshore exploration campaign, acquiring some 6,000 kilometres of seismic data and, during 1983 and 1984, drilling two wells. None of these wells was a commercial discovery. Between 1995 and 1997, an integrated team of KOC and Shell explorers undertook a review of the hydrocarbon potential of Offshore Kuwait. In order to establish an integrated sequence-stratigraphical framework for the prospective Lower to Middle Cretaceous interval, a quantitative biostratigraphical study was made. Some 790 biostratigraphical analyses (10% core samples; 90% cuttings) from eleven wells were carried out: the nanno-fossil data was particularly important in providing accurate chronostratigraphical calibration, and this data has been used to constrain a “Time-Rock Synopsis”. KOC’s lithostratigraphical nomenclature proved to be basically sound and has been maintained as the basis for the present stratigraphical framework. However, the study revealed the existence of two substantial and hitherto unsuspected hiati: one between the Ratawi and Zubair formations of Early Valanginian to Mid-Hauterivian age; and the other, representing the whole of the Early Albian, within the Burgan Formation. This latter result, if it can be further substantiated by more exhaustive study in the onshore area, would neccessitate a re-definition of the Burgan Formation and the erection of a new formation to describe the clastic sequence of Late Aptian age which lies between the Early Albian hiatus and the top of the Shu’aiba Formation, and which has hitherto been included within the Lower Burgan Formation.
Performance Evaluation Of Horizontal Wells In A Tight Carbonate Reservoir. Abstract This paper presents a case study of evaluation of the performance of horizontal wells drilled in a tight carbonate reservoir in Kuwait. Successful wells were those that intercepted natural fractures. A methodology was developed to define the reasons for the performance of horizontal wells. The methodology involved use of geological, petrophysical geochemical, transient test, rock, and fluid properties to develop a numeric simulation model. Conclusions regarding well performance were made by using a newly developed analytic simulator and the numeric model. While the analytic simulator provided rapid rate forecasts, the numeric simulator gave insight into the causes for unsatisfactory well performance. For example. well placements within the bed, low-permeability rock, and unfavorable relative permeability characteristics all contribute to the rapid rate decline and the associated increasing gas/oil ratio (GOR) production. We developed cyclical production and oil injection schemes to address the high-GOR production problems. In the first scheme, a well is produced and shut-in alternatively to preserve the reservoir energy, and in the second, oil is injected periodically to minimize the gas saturation. Both methods increase the ultimate oil recovery. Introduction Horizontal well technology has evolved rapidly since pioneering drilling efforts were begun in late 1970s in the Raspo Mare Field offshore Italy. In the US, spawned by successes at the Austin Chalk formation in East Texas since 1985, the horizontal drilling activity gained considerable momentum. Austin Chalk happens to be a tight carbonate with extensive vertical and sub-vertical fracturing. Despite publication of numerous successful case histories, Beliveau, while compiling a major operator's world-wide horizontal well efforts, observed that many-fold production increases do not often materialize because of incomplete knowledge of reservoir heterogeneity before drilling. North Sea's Ness field is also a case in point. Combined industry experiences suggest that the success of horizontal wells lie in selecting the right candidate reservoir. Fayers et al. summarizes some of the reservoir engineering issues that need considering while evaluating horizontal well prospects. Besides gaining productivity increases in general, horizontal wells have enjoyed success in combating coning or cresting of water and/or gas, in accessing by-passed oil and multiple flow units, and in converting resource into reserves, such as those in heavy oil and tight reservoirs. Examples of high-permeability sandstone reservoirs where water coning has been mitigated include Troll field in the North Sea, Prudhoe Bay field in Alaska, Safaniya field in the Middle East, and those in offshore west Australia. Similarly, horizontal wells in Rospo Mare, the Karsted limestone reservoir, have enjoyed considerable success in mitigating water coning. While horizontal well successes are often presented in various forums, the associated failures do not gain as much publicity. Generally speaking occurrences of failure are high with carbonate reservoirs where successes depend largely upon horizontal wells intercepting natural fractures. South Kuwait's Mauddud reservoir in discussion is a low-permeability carbonate with sparse fracture development. Successful exploitation of reserves with horizontal wells in similar reservoirs has not been reported. Only the Dan field in the North Sea and the Kharaib B reservoir offshore Qatar have permeabilities that are comparable to this reservoir; that is, 1 to 10 md. However, they are much thicker and lend themselves to hydraulic fracturing because of confining shale barriers. Besides accessing fractures, the fluid-rock interaction with changing fluid saturations plays a critical role in the success of long-term producibility potential of a well. Thus, initial screening criteria should encompass this aspect before drilling horizontal wells. P. 601
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