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.
Well integrity assurance and zonal isolation, are the main pillars for any oil and gas well, it was a practice in the past to evaluate cement behind casings for casings smaller than 13 3/8 inch, however with the increase in drilling deeper and more challenging wells, the need for evaluating cement behind larger and thicker casings became a necessity. Different logging companies have invested in their existing cement evaluation services and upgraded their tool designs, specifications, and increased tool operating range to address the larger and thicker casing requirements. By mid-2016, the upgraded tool measurements range was extended to evaluate up to 22-inch. KOC in South-East asset started developing their Marrat deep reservoir back in 2018, these wells are designed with large surface casings ranging between (18 5/8-inch and 24-inch) across their main reservoirs (Burgan) and the shallow water and gas bearing formations (Dammam, Radhuma, Tayarat, and Mishrif). Dammam, Radhuma, Tayarat, and Mishrif formations, feature a highly fractured carbonate reservoir and comprise corrosive water and trapped gas pockets. The corrosive water and the trapped gas pockets pose future potential well integrity risks in the field, which implies the need for proper zonal isolation throughout the well and the field lifespan. These formations also comprise a low formation frac gradient, that raises the requirement for low-density cement ranging from 8.5 to 10.5 PPG to overcome the shallow loss zone. The newly developed extended range for the ultrasonic cement evaluation tools can cover up to 18 5/8 inch surface casings for KOC, however, some additional tests, work, and modifications were required to accommodate the 24-inch casing, which will be discussed later in this paper.
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.
Drilling wells in some locations in the Greater Burgan field in Kuwait, can demonstrate significant challenges across the intermediate section. Part of these challenges are combining the carbonate formations with the weak unstable Ahmadi shaley formations at the bottom of the section. This makes it challenging to drilling engineers and difficult to balance between natural mud losses across the carbonate formations and weak shale that requires higher mud weight. Adding to these challenges, the limited surface locations in the field, that forces the well design trajectory to be deviated, which makes the mud window even smaller and shifts it higher. Zonal isolation across this interval adds an additional challenge, as it will prevent gas and liquid to escape from high pressure deeper zones to shallow lower pressure zones and probably to surface, which potentially may cause well integrity issues in the future. This paper represents a case of formation collapse on a casing prior to cementing operation, how it was detected, how it was handled and how successfully the well was completed.
A geomechanical evaluation and monitoring programs was conducted in order to reduce non-productive time and drilling complications while drilling in a tectonically stressed area of Kuwait. Offset wells had experienced problems related to the tectonic stresses and associated faults, fractures, complex structures, and anomalous pore pressure. Additional challenges were faced due to complicated and highly deviated well designs where planes of weakness in the formation being drilled and their relative angle with respect to the well path become crucial factors in assessing stability of the borehole. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, are found to be the root cause of wellbore instability across reactive shale and other problematic formations especially during drilling of highly deviated wells. To successfully achieve the above objective, it was prudent to be armed with proper assessment and understanding of wellbore stability along with optimizing the most appropriate drilling strategy. Five offset wells were assessed from Geo mechanical point of view in the area in order to simulate the back analysis of the borehole collapse in the unstable zones. The previous wells experience showed a high risk to drill the shales and depleted reservoir formation in one section, causing a high ECD in depleted reservoir which dramatically led to severe losses. The planned well was monitored in real time through the control of the ECD and drilling parameters. Since shales in that section are unstable and tend to be plastically deformed, high mud weights were typically used. Based on the geomechanical inputs of the wellbore stability while drilling, new casing strategy was formulated taking into-account the wellbore stability input, drilling parameters and the mud rheology. The shale section was isolated with separate casing and well was successfully drilled to TD without any drilling complications and minimum Non Productive time. Geomechanical modeling and real-time monitoring allowed the well operator to overcome serious drilling hazards and optimize the drilling practices. This application promises to open the prospect of drilling similar wells without complications and reduced NPT in Kuwait.
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