Prehydration -the reaction between anhydrous cement and water vapour -has deleterious effects on engineering properties such as compressive strength, workability and setting time. This study assessed changes in the engineering properties of CEM I Portland cement exposed to relative humidities (RHs) of 60% or 85% for 7 and 28 days. Thin layers (no more than 2 mm thick) of CEM I 42.5R cement were exposed to controlled RHs of 60% and 85%, followed by assessment of compressive strength, setting time and workability. These measurements were complemented by characterising the prehydrated anhydrous cement using isothermal calorimetry, scanning electron microscopy, X-ray diffraction and thermal gravimetric analysis. Following prehydration at 60% RH, conventional hydration resulted in a negligible reduction in strength development plus a decrease in workability and increase in setting time. At 85% RH, compressive strength was greatly reduced, particularly at early ages. There was also a greater loss of workability and increase in setting time.

It is a challenge to drill in highly deviated or horizontal holes with high differential pressures. Wellbore instability, differential sticking and mud loss are frequently encountered problems while drilling slanted wells in Kuwait across shale and sand series. Drilling became more challenging with considerable non-productive time. Therefore, it is necessary to identify a fluids 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 shale and sand series 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 minimize 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 development 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 a series of laboratory tests. Drilling and logging were successfully performed for the first time in the commingled 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 some successful applications of the nano-size deformable polymer in OBM to drill highly depleted formations in HTHP wells managing up to 3500 psi overbalance across highly permeable formations.

Shale stability and differential sticking are the main challenges while drilling through shale and sand sequences. Conventional mud systems cannot always provide the required wellbore stability and sustained high overbalance, which has led to an increase in use of ‘customized fluids’. Offset wells were reviewed to identify the issues while drilling this challenging trajectory through troublesome stressed Zubair shale and sand sequences. This review revealed serious well-bore instability, pack offs, differential stuck pipe leading to the loss of downhole tools and sidetrack operations. Traditionally, oil-based mud (OBM) have been used while drilling these formations with high NPT hours. Due to necessity of comingling two sections in a single section, it was necessary to identify a fluid's solution, which can provide good borehole stability. A customized drilling fluid system was designed by using deformable sealing polymer (DSP, deformable size) in conjunction with Synthetic Resilient Graphite and Sized Calcium Carbonate (CaCO3) in conventional OBM. These Nano particles effectively plug the pore throats and minimized the fluid invasion, which was confirmed by particle / permeability plugging tests under down hole conditions to overcome below challenges. Improve hole stability through stressed shale formationsMinimize risk of differential stuck pipe across low pore pressure formationsMitigate induced losses by utilizing unique wellbore-strengthening techniqueEnhance hole-cleaning efficiency at critical angle Drilling, logging, running and cementing liner was successfully completed in the commingle section without any incident. There was no NPT related to well-bore instability or differential sticking tendency reported. Very low torque and drag was observed in addition to enhanced well-bore cleaning in the high angle section. This paper will present the success of the deformable sealing polymer in OBM utilized to comingle Upper Zubair shale and Ratawi shale with case histories for reference.

To optimize production from a key reservoir, obtaining a core sample with minimum fluid invasion and damage was necessary. In addition, operational nonproductive time (NPT) related to drilling challenges, such as interbedded formations of varying formation pressures, wellbore instability in the reactive, stressed shale sections, and hole cleaning concerns, needed to be mitigated. This paper describes the design of the drilling fluid and its performance in the field. After completion of the first dump flood water injection well drilled using an 80/20 conventional nonaqueous fluid (NAF) weighted with barite, low injectivity was observed, which led to acquiring cores to analyze permeability and porosity along with the change in mineralogy resulting from long exposure of the reservoir in the water zone. A 70/30 organophilic clay-free (OCF) NAF was selected to mitigate equivalent circulating density (ECD) risks and minimize damage. Proprietary software was used to customize the bridging design, which was verified during laboratory testing, and to help ensure adequate hole cleaning with the customized low-ECD fluid. The engineered OCF NAF contained no damaging materials, such as barite, asphaltic material, or organophilic clay. OCF NAFs are well suited to low-ECD drilling operations because they are more resistant to weighting material sag than conventional NAF systems of similar rheology. This is a product of the high gel strengths developed, even in low-rheology (low-ECD) fluids. Downhole pressure fluctuations are low because these gels are fragile and break easily. For the well in which this OCF NAF was used, drilling, coring, and logging operations were successfully completed without incident. Four cores were acquired with minimal damage compared to the previous wells resulting from the engineered design of the bridging material and fluid-loss control polymers. In addition, there was minimal erosion to these four cores, which was a result of the low-ECD fragile gel fluid used. The fluid-loss control properties of the fluid were also effective in strengthening the wellbore and eliminating differential stuck pipe tendencies that had been observed in previous wells. The fluid properties resulted in minimal ECD, and the OCF NAF displayed excellent suspension along with improved pressure management; no pressure spikes occurred while breaking circulation. There was no NPT related to wellbore instability or any of the drilling challenges previously identified. This unique organophilic clay-free and organolignite-free drilling and coring fluid relies on a specialized technology involving an interaction between the emulsifier package and the polymer additives in the fluid. This provides the behaviors needed for reliable weight material suspension and suitable hole cleaning properties in a low-ECD drilling fluid. Together with the appropriately designed bridging package, the OCF NAF provided a better understanding of the reservoir characteristics by delivering the core with minimal damage.

One of the common challenging drilling environments is harsh rocks which require specially tailored drill bit design features to deliver the maximum drilling efficiency. The interbedded nature of harsh rock formations in combination with high rock strength results in reduced bit aggressivity and premature bit wear which increases the drilling costs. This paper presents field testing a new drill bit technology that addresses those challenges. The bit was deployed and tested in a vertical application in an exploratory well in North of Kuwait and achieved the fastest penetration rate in the application. Numerous full scale pressurized laboratory tests were conducted on different rocks including limestone, sandstone and shale to develop and validate a new altered cutter geometry designed for carbonate applications. The main target of the simulations was optimizing the cutting action of the PDC cutter while drilling a carbonate formation. This resulted in development of altered cutter geometry designed for fracturing and shearing, offering improved effectiveness in medium to hard formations such as carbonates and clastic rock and more efficient cutting action than conventional round cutters. By creating subsurface cracks that propagate to the rock surface, the new cutter allows creation of thin and uncondensed cuttings, making an efficient use of energy. The first 12¼ in. 6 blades 16mm configuration bit equipped with the new cutter geometry in conjunction with a stiff rotary BHA was tested in a vertical exploratory well in Bahrah Field, North of Kuwait. The bit delivered improved performance by completing a total interval of 2,655 ft from 5,915 ft to 8,570 ft in 60 hrs resulting in 44.2 ft/hr rate of penetration while drilling from Mutriba to Burgan formations. The bit demonstrated excellent durability with a dull grade of 1-1-WT-A-X-I-NO-TD after drilling in a highly interbedded harsh application where the lithology consists mainly of limestone, shale & sandstone. The performance capability was further confirmed when the same bit drilled the second well to section TD completing a total interval of 2,630 ft with ROP of 68.7 ft/hr. achieving the top record run in north Kuwait vertical application in Bahrah field. The 12¼ in. bit with the non-planar cutters surpassed the average rate of penetration (ROP) for the same application in Bahrah Field by 76% saving the operator significant drilling time and making this bit design the top performing drill bit in the field. As a result of the continuous research and field testing, the new cutter technology has drilled more than 10 million feet globally proving its success and efficiency in a wide range of applications.