The Jurassic reservoirs of deep wells in Kuwait have traditionally been drilled with OBM. Barite is utilized as the weighting material in the OBM resulting damages to these reservoirs, thereby reducing the productivity to a significant extent. The higher oil to water ratio (95/5) of OBM limits the possibilities of identifying the micro fractures in reservoirs due to the limited conductive medium in OBM. Potassium formate WBM, with Manganese Tetraoxide as weighting material was successfully applied in HPHT wells overcoming these limitations. K-Formate brine was utilized up to maximum density of 12.5 ppg to reduce the impacts of solids in the mud. For the first time, maximum mud weight of 17.8 ppg was achieved operationally using micromax (Mn3O4) in this WBM. Also, for the first time in Kuwait, this kind of fluid was used to drill the section with the inclinations above 60° in deep wells. As a result of using K-Formate WBM in the reservoir sections, production increased significantly when compared to the wells drilled with OBM and barite. Wells were simulated easily without the presence of barite. Water based conductive medium gave better quality of image logs. Unlike other WBM's, K-formate WBM was stored for long periods, over a year in the mud plants without any damage to the mud properties. Recycling reduced the overall fluid costs in the subsequent wells drilled with K-formate WBM. Environmental damage due to the OBM spills and cuttings were completely avoided; K-formate WBM is highly bio-degradable under atmospheric conditions and is environmentally friendly. The experience and success gained with its use on the initial wells led to the planned usage of this WBM on all deep exploratory wells. This paper explains the experiences gained and the achievements made over the years with K-formate WBM used for drilling the deep HPHT wells.
It is a challenge to drill in highly deviated or horizontal holes across the highly depleted formations. Wellbore instability, differential sticking and mud loss are frequently encountered problems while drilling a depleted reservoir in deep HTHP wells in Kuwait. Long-term production caused formation pressures to be highly depleted, and drilling became more challenging with considerable non-productive time. Therefore, it is necessary to identify a fluid’s solution when other options with casing zone isolation are not viable. Traditionally, oil-based mud (OBM) was used while drilling these formations with limited success. A customized fluid system was designed to overcome the issue of high overburden pressure in depleted formations targeting effective bridging, minimizing pore pressure transmission and strengthening the wellbore. A nano-size deformable synthetic polymer, along with sized calcium carbonate and graphite, was identified to effectively plug the pore throats and minimized the fluid invasion, which was confirmed by particle plugging tests. A well section was identified to comingle the highly depleted and pressurized formations. This was the first attempt on a high-angle well with deep drilling operations in Kuwait and was performed to facilitate the successful drilling of the reservoir. Traditional OBM was converted to a customized fluid system using a nano-size polymer and sized bridging additives based on proprietary software selection and series of laboratory tests. Drilling, coring and logging were successfully performed for the first time in the commingle section without incident. There was no wellbore instability or differential sticking tendencies, less torque and drag, as well as enhanced wellbore cleaning in the high-angle sections. This paper also presents the some of the successful applications of the nano-size deformable polymer in OBM to drill highly depleted formations in HTHP wells managing upto 3500 psi overbalalnceacross highly permeable formations.
Deep wells drilled into the Jurassic formations of Kuwait have long utilized oil based mud (OBM) with barite as the weighting material. However, barite caused considerable damage to the reservoir sections, resulting in reduced production rates. The high oil content in the OBM also prevented recording of good quality image logs, which was necessary to identify the micro-fractures in the reservoir. To overcome these issues, it was necessary to use a water based mud (WBM) with non-damaging weighting material suitable for high pressure conditions.The existence of high pore pressures and a requirement for mud weights up to 18.5 lb/gal in these wells ruled out the use of conventional WBM. Laboratory tests conducted using a fluid based on Potassium Formate (K-Formate) brine weighted with Manganese Tetraoxide (Mn 3 O 4 ) as an alternate weighting material. This fluid was successfully applied in a number of deep wells, resulting in increased production rates, up to three times higher than the wells drilled with OBM. Damage to the reservoir was considerably reduced as the wells were easily activated. High quality image logs were also recorded which was not previously possible with OBM. K-Formate-Mn 3 O 4 fluid is a non-corrosive, biodegradable, environmentally friendly fluid, capable of long term storage without degradation of mud properties and recyclable, which reduces fluid cost in subsequent wells. This paper will review the case histories of twelve deep exploratory wells where the K-Formate-Mn 3 O 4 fluid was applied successfully. Issues including, high rheology encountered while increasing the mud weight using Mn 3 O 4 , fluid related complications in drilling and solutions developed to overcome the problems will be discussed in detail. Lessons learned in each deep high pressured well, mud loss scenarios and well control issues will be discussed.K-Formate-Mn 3 O 4 based drilling fluid has been highly successful in drilling high pressured Jurassic reservoirs in Kuwait. Following the success of the fluid in these wells, it is now being planned to apply in all future deep exploratory wells.
Drilling deep wells in Kuwait has become a challenge due to excessive overbalance pressures up to 3,500 psi applied across a highly permeable sandstone/shale formation. High differential pressures leading to tight hole, string stalling, differentially stuck pipe and induced losses contribute to considerable nonproductive time. The existence of a high pressure salt zone below this interval and a seven casing string design removed the further option of zonal isolation by casing. Traditionally, oil based mud with Calcium Carbonate of different sizes was used to reduce fluid invasion, but with limited success. A customized fluid system was designed to overcome the issue of high overbalance pressure targeting improved bridging, minimized pore pressure transmission and wellbore strengthening with increased hoop stress. Software modelling and permeability plugging tests were performed to evaluate the fluid behavior under downhole conditions and to predict the characteristics of induced micro fractures based on rock mechanics. Porosity, permeability and induced micro fractures were considered to optimize the bridging mechanism. These results identified a synthetic deformable sealing polymer combined with sized graphite and ground marble showed considerable improvement in minimizing filtrate spurt loss without altering the rheological parameters and stability of the OBM.A inclined well in sandstone/shale formation was selected for the application after suffering multiple wellbore instability and differential sticking incidents, resulting in more than 800 hours of non-productive time and a sidetrack. The new inclined section was successfully drilled with a stable wellbore, smooth trips, and no tight hole or sticking incidents. The borehole remained completely stable, even after 16 hours of 13 5/8Љ casing string suspended in 16Љ open hole without circulation.This paper analyzes the historical problems encountered in this sandstone/shale formation, and presents the solutions developed based on these problems and case histories of the successful field application of this customized fluid.
A blowout in an HPHT deep well posed a major challenge while designing the relief well which was required to bring the well under control. For the relief well it was necessary to carry out a comprehensive well design and operational planning, identification and mobilization of necessary equipment in a short time. This paper will describe the preparations made for this type of relief well in the region. An existing deep J-shape directional well, suffered a blow out while drilling a deep Salt/Anhydrite formation where formation pressures were extremely high. The blowout well was surrounded with many other producing facilities, drilling activities and inhabited areas. The main challenge was to choose a suitable location as close as safely possible, in such a congested mature oil field, taking into consideration all the safety aspects such as wind direction, surrounded wells, flame and heat created from blowout well, etc. The other main well challenges concerned; well placement, intercept with blowing well and dynamic kill. This paper will concentrate on the aspects of relief well design and planning. It will cover all related topics, such as; number of relief wells planned, surface location choice, potential drilling problems, directional design, detection of the blowout well, and placement philosophy. It will include a discussion on the specialized directional and ranging equipment and techniques needed to perform the critical operations of locating, following, and intersecting the blowing well. All aspects concerning HSE will be discussed in detail. The paper will present these in a case history format covering the design process, operational planning, and a description of well operations.
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