The current study presents elastic properties model for Fulla Oilfield in northeast of Block 6 in south of Sudan. Due to the poor formation consolidation and relatively viscose fluid, reservoirs may predictably produce massive amounts of sand and numerous troubles were found in the field as a result of sanding. No documented researches were found to introduce good parameters for rock strength and rock failure conditions through the field. Therefore, an accurate technique for predicting rock failure conditions may yield good profits and improve the economic returns through preventing sand production from the formations. General correlations were presented to accurately describe rock strength parameters for the field; the work utilizes the application of the wireline porosities to be used as a strength indicator through the combination of rock mechanical theories with the characterization of Fulla oilfield. Log porosities (density, sonic and neutron) were calibrated with the core measured porosity, and the best matching porosity were correlated with the dynamic calibrated strength parameters by different correlations. The results support the evidence of the use of porosity as an index for mechanical properties; power functions were found more reliable than the exponential functions, and can be used with a high degree of confidence; also it is more accurate than the Shale Index model presented in pre-vious work for same field; however, the result does not support the direct linear expression pre-sented in the literature for other field due to the variations in the field conditions.

Drilling the 16-in. section in Minagish field wells in western Kuwait is among the most challenging well sections. Challenges include drilling through severe loss conditions, destabilized shale, and deteriorating hole conditions. These conditions can result in hole collapse or lost in hole of the drill string that requires sidetracking. The objective of project presented in this paper was to develop an engineered solution to drill through the difficult zones, lessen nonproductive time, and reduce the total well cost. The solution proposed was to use casing-while-drilling technology with a drillable bit and drill through the fractured dolomitic limestone and sandstone formation while simultaneously setting casing. The drillable casing-while-drilling bit was specifically designed and engineered to conform to the formations in the field. The drillable casing-while-drilling bit is manufactured with a material that can be drilled out with either conventional roller cone or fixed cutter bits. A plastering process was used, which smears the cuttings generated by drilling against the borehole wall, seals the pores or fractures in the formation, and helps reduce fluid losses while maintaining well integrity. The first successful 16 × 13.375-in. casing-while-drilling job in Minagish field reduced well delivery time for the operator and saved 27 rig days with substantial savings in the total well cost. The section was drilled successfully while encountering total mud losses through fractured dolomitic limestone and sandstone formations. Continued drilling managed to reduce losses with 30 to 50% returns and reached the target depth. Preventing the risk of losing the bottomhole assembly in the hole and alleviating the use of multiple cement plugs saved additional cost for loss-cure plugs to heal the loss-prone formations. After reaching the target depth, cementing, pressure testing of the casing, and drillout of the drillable casing-while-drilling bit using a rerun fixed cutter bit were performed successfully. On an average, eight wells are drilled per year in this field. With the successful implementation and the savings obtained by using this casing-while-drilling technology in the first test well, there is the potential for substantial annual cost savings, help the operator deliver wells in less time, and eventually increase production by increasing the number of wells drilled per year.

Conventionally, the Cretaceous shale in North Kuwait is drilled at a high angle with an invert emulsion-based drilling fluid. Environmental and operational considerations required the development of a water-based system capable of closing the performance gap between invert-based and water-based drilling fluids. A customized high performance water-based mud (HPWBM) was used successfully where previous attempts with alternative water-based mud (WBM) had experienced significant challenges. Key well challenges included wellbore instability with caving shale and the potential for differential sticking and pack-off. A HPWBM enhanced with an innovative sealing polymer was customized to maintain optimal drilling performance by minimizing shale erosion in these highly dispersible clays, while also decreasing pore pressure transmission via the micronized sealing polymer. These clays, having moderate reactivity, are prone to dispersion when there is communication between water or water-based mud. The improved levels of fluid invasion were optimized using the particle plugging apparatus (PPA) to achieve the minimum interaction between the fluid and shale. The formulation was finalized, based on laboratory testing, to optimize the bridging and inhibition package for the formations drilled. After finalizing the formulation, the control points were agreed upon between the operator and service company to ensure that the required inhibition and bridging package were implemented on the well and to define success criteria. Drilling was completed, and the casing was run successfully with no incidents; the fluids parameters were maintained to effectively stabilize the hole while drilling through geomechanically stressed formations in a challenging azimuth: the direction of minimum horizontal stress. The addition of the sealing polymer to the already-inhibited HPWBM effectively stabilized the wellbore, which helped reduce the caving tendency of the stressed shales. The two intervals were drilled and cased in two days less than the average time required with an invert emulsion fluid. There was no nonproductive time (NPT) related to wellbore instability, and differential sticking was avoided by the customized bridging and sealing across the depleted zones. This paper discusses the design, technical features, and benefits of a HPWBM system, enhanced by the addition of an innovative sealing polymer, which helped successfully drill the 12 1/4- and 8 1/2-in intervals. A customized HPWBM provided good shale inhibition, mechanical stability, and excellent lubricity, customizing the conventional fluid for the increased challenges posed by the stressed shale.