Unwanted water production is a major challenge in the horizontal wells in the Greater Burgan field in Kuwait. The long lateral sections and the presence of heterogeneity lead to uneven sweep of hydrocarbons. Greater Burgan has over 60 horizontal wells to date. Initially they produced dry oil and up to the expectation but soon the water cut increased in a number of wells and avoiding water break through became a major challenge. Burgan sandstone is a highly productive reservoir and the permeability variation is huge from less than a Darcy to a few Darcy. Thus, the horizontal wells have uneven flow profile and subsequent coning and cresting effects resulting in bypassed oil and poor recovery. To have a better down-hole water management in horizontal wells a number of options from chemical water shut-off and isolating the toe side using packers to use of straddle packers in the middle and heel side of the horizontal section were tried. However, the use of Inflow Control Device-ICD proved to be the best option to restrict and slow down and contain the water production by creating additional pressure drop and achieve better sweep efficiency. The first ICD completion in the Greater Burgan field and in KOC was implemented in a sidetrack well in 2007. To date the well is flowing with 45% water cut which is almost constant from the beginning for 7 years now. It resulted in a net gain of 2400BOPD from this well. This paper will describe this case history, how the system was designed, completed, and monitored, and the successful results achieved for over 7 years. This successful use of ICDs for water conformance lead to more applications in Kuwait and will give a good understanding for the future use in other areas.
The Mauddud Formation in the Greater Burgan field is a thin carbonate reservoir with very low permeability but with moderate to good porosity and variable fracture density. The formation could be divided into three distinctive layers, based on the structural and digenetic complexities. Production in Mauddud wells show rapid decline due to tight rock matrix (low permeability). This decline is associated with an increase in Gas-Oil Ratio (GOR) as reservoir pressure falls below the bubble point pressure near the wellbore. Horizontal wells were drilled in an attempt to develop the Mauddud Formation targeting sweet zone. Most of the wells were located in a relative structural high on the up-thrown blocks of the North and Eastern flank of the Greater Burgan field that had the highest likelihood of intersecting fractures. They are mostly adjoining the major faults. There are now around 40 wells drilled in Mauddud including horizontal and multilaterals, most of which became non-producers due to above reasons. A study has been carried out to evaluate opportunities to revive these wells through available and new technologies in the industry. A detailed geological study incorporating all the available data was carried out initially. Wells were screened for stimulation by using various proven new technologies. Acid Frac, Stage Frac, near well bore SurgiFrac and Matrix Acid techniques have been applied with varying results. Advanced placement technique like distributed temperature profiling was used in some of the jobs. This paper presents the details of the application of the above mentioned technologies, to the candidate wells and discusses the results. The success of some of these technologies opened up new opportunities for a new beginning to revive the closed wells completed in Mauddud Formation.
For managing limited resources, short and medium horizontal sidetracks offer feasible options for non-conventional well work-over. Sidetracking into horizontal lateral is preferred over other options due to improved productivity. Many short-radius horizontal sidetrack wells with high Dog Leg Severity (DLS) have successfully been drilled and completed with Inflow Control Device (ICD) in carbonate reservoirs in the Middle East, however in case of sandstone reservoirs it poses a great challenge. This technology, which envisages short and medium radius horizontal sidetrack from existing well bore for optimal utilization of asset, was applied in a sick well from Greater Burgan field in Kuwait. A window was cut in existing 7″ casing and 6 1/2″ drain hole was drilled up to 6016′ MD. Initially this well was planned for sidetrack into main sand with maximum 35° DLS and feasibility study was done. But due to mechanical complications during work-over it was kicked off shallower, cutting shale above main sand, and the final well trajectory was maintained with maximum 23° DLS. The horizontal lateral was completed with 4 ½″ ICD and seven numbers of mechanically set open-hole packers for zonal isolation. The well completion with this technology with high DLS in a sandstone reservoir is probably the first time in the world. This paper will describe and present the case history of the application of this technology; the challenges faced during work-over, drilling of the drain hole with sand-shale contrast and the smooth running of completion assembly with high DLS. After work-over the well was put on production in May'08. As on date it is flowing with 45 -55% water cut which is almost constant since then, resulted in a net gain of 2400BOPD from this well. This successful sidetrack leads to more applications for exploiting heterogeneous reservoir in the Middle East Region.
The Greater Burgan Field consists of three sub fields (Ahmadi, Burgan and Magwa). Drilling commenced in this field in 1938 and it went on stream in 1946. Most of the production comes from a giant oil reservoir in a siliciclastics depositional environment. This giant oil reservoir has intercalating sand shale sequence with the upper part having mixed lithology. Co-existing together are argillaceous glauconitic sandstones, calcite, dolomite and anhydrite with pyrite and siderite. With increasing demand of oil in the world, it has become necessary to improve oil production. As a result, the various field development assets of Kuwait Oil Company (KOC) are tasked to increase the number of horizontal wells in order to access thin reservoirs in the field. This has prompted these teams to increasingly rely on Logging While Drilling (LWD) services as well as improved geosteering practices in order to efficiently access the untapped energy resources buried several thousand feet below the earth's surface. Evaluating these wells becomes an issue especially if the wells are drilled in areas that might add to the reserves of the asset. Resistivity anisotropy is a major issue, especially if it occurs with influence of other bed boundary effects like resistivity of adjacent beds or polarization horn effects. Water coning issues in the field makes it even worse to interpret the resistivity data as they become spiky. Complexity of the resistivity signature in a mixed lithology environment makes petrophysical evaluation difficult. With the recent introduction of the Multi-Function LWD tool where most of the basic measurements are collocated in one LWD collar, it is now possible to make measurements with similar environmental influence prior to significant invasion of the formation. In addition, the introduction of capture gamma ray spectroscopy and formation sigma in real time has improved the petrophysical evaluation of this complex resistivity environment with mixed lithology in wells that are difficult or even costly to consider wireline logging. This paper aims at highlighting horizontal well drilling issues occasionally encountered in the Greater Burgan Field and the recent introduction of the Multi-Function LWD service to help address these formation evaluation issues.
Drilling in thin reservoirs is challenging task. But with easy pockets gone the reservoirs left are less than 5 to 10 feet and it becomes difficult to steer well exclusively in the sweet spot or sand in thin payzone. It is this reservoir which offer task to drill horizontal well and produce maximum where otherwise it would be difficult to produce even 200-300bopd from this thin layer of silty shales. Moreover the thin beds are like appearing or vanishing as we drill ahead due to facies change. This needs complete attention till the well reaches Target Depth (TD). Even a small fault of sub-seismic nature of 2 feet throw can offset the well from the sweet zone. But with advanced logging tools used in two wells helps to understand the nature of lithology and its productivity. Best application of this tools are in silty shales in Burgan Sands Upper (BGSU) which generally show high GR and often this leads to misjudgment of well not being in sweet spot. Logging While Drilling (LWD) logs and inversion was used whether the well is in productive zone or not. The LWD tools now have Azimuthal GR, density and resistivity. This gives a holistic picture of the lithology in the roof side or the bottom side of the lateral section. The wells under discussion were drilled with such advanced version of distance to boundary tool. After well was steered till TD, the data was processed by Petro-physicist to indicate possible payzone to decide completion. But due to high GR which is often prevalent in Burgan Sand Upper (BGSU) the entire well bore was not getting classified as potential payzone. But after looking the inversion and all LWD data sets it was conveyed that the Inflow Control Device (ICD) can be lowered for entire well bore length. As an outcome advanced ICD was lowered also against high GR zones which otherwise were not getting classified as potential payzone, and well were completed. The well was put on production starting with 1300 BOPD on 32″ choke and still after 18 months continues to produce. PLT results show that the zones indicating high GR and with poor log properties were also contributing oil. The paper discusses these wells and utilization of complete data set acquired at time of drilling and taking completion decision accordingly. The output of data of LWD has been fully utilized to complete the well successfully and given the confidence of doing so in other wells. In fact this experience was used in another similar looking well with unfavorable parameters and successfully completed.
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