Resin is a solid-free fluid that can penetrate tight narrow annuli, cracks, or fissures previously inaccessible to conventional or fine cement slurries. Furthermore, this resin system can transition from a liquid to a solid phase through crosslinking reactions consisting of stages of low-viscosity liquid, high-viscosity liquid, viscoelastic solid, and finally forming a solid crosslinked three-dimensional (3D) polymer network. The resin continues to transmit hydrostatic pressure to the formation until an impermeable barrier of cured resin creates a highly ductile material that provides resistance to liquid or gas penetration. During the completion of a well in Western Desert, Egypt, pressure tests revealed a leak with a 1-bbl/min leakoff rate at 1,600 psi in the 4.5-in. liner hanger assembly, which was caused by liner top packer failure. This issue required fast remediation to maintain the economic value of the well. After careful evaluation, the resin sealant system was determined to be the best solution. The resin was tailored to meet the well requirements for placement across the leakage area by applying a squeeze method, successfully stopping the leak. A 4,000-psi pressure test proved the integrity of the well after the resin placement. This paper discusses other solutions considered during this case study and provides details about the process of elimination of each, as compared to resin. The resin sealant system provided a dependable barrier and enabled operations to continue without issue. This intervention enabled the well to successfully meet its original objective

In a world where energy is a major concern, the revolution of shale gas globally has triggered a potential shift in thinking about production and consumption that no one would have expected. The enormous shale gas resources identified today are becoming game changers in many developing countries. The booming economy of India is seeing a significant increase in its energy demand, with industries establishing new footprints in the western region of the country. Operators are venturing into deeper and harsher conditions (HP/HT environments) to tap those resources. Even though shale gas is now found globally, it is still described as an unconventional source of hydrocarbons. This is because the extraction of shale gas is tricky and challenging. To unlock the unconventional gas reservoir most of the wells are horizontally drilled and hydraulically fractured. This process has a strong impact on cement bonding across the section. Firstly, the cement needs to provide an effective barrier in the annulus around the casing, which has been horizontally placed. Secondly, cement has to withstand various mechanical loads during hydraulic fracturing and ultimately over the life of the well. The present study covers the Navagam field located in the Ahmedabad block of North Cambay Basin. Cambay Basin is bounded on its eastern and western sides by basin-margin faults and extends south into the offshore Gulf of Cambay, limiting its onshore area to 7,900 mi2. The operator's western asset had already deployed its resources on evaluating the data to assess the potential shale gas in the Navagam block in the Cambay Basin. This paper highlights successful cement placement in an unconventional shale gas reservoir in onshore western India. It was crucial to understand why early exploration wells in the area resulted in poor initial zonal isolation in order to refine the asset development model for future wells. Based on these models, a mechanically modified resilient cement system was engineered. Subsequent exploration wells were then cemented with the resilient cement system to allow for dependable zonal isolation of reservoir bands permitting the accurate determination of discrete reservoir geomechanical properties within the overall reservoir target.

The Fuling shale gas field in China was discovered in 2012 and is a quality high pressure natural shale gas reservoir in the Longmaxi formation. Since then, more than 500 wells have been drilled and are being produced. However, over the period there has been a reduction in production and therefore refracturing is needed to maintain production. A new casing-in-casing method of re-constructing a new wellbore inside the legacy wellbore for re-fracturing was introduced and successfully executed. The producing wellbore has a series of perforations along the casing of the horizontal section. Wellbore re-construction is required to isolate all these perforations and allow a plug-and-perf fracturing process in the new wellbore. It was planned to run a 3.5 inch casing into the existing 5.5 inch casing and cement it. A dependable cement barrier in this extremely tight annulus is required to carry on future re-frac operations. Computational fluid dynamics and stress modelling were performed to optimize the slurry density, rheology, mechanical properties and based on various iterations tailored ceramic centralizers were proposed to achieve zonal isolation objectives. The top of cement (TOC) in the annulus is required to be above the topmost planned perforation. The remaining 3.5 inch casing above the designed depth was disconnected and pulled out. A new 5.5 inch X 3.5 inch wellbore without any leaks to the existing perforation was constructed. The wellbore was reamed to bottom, and the losses were treated prior to cementing. Tailored ceramic centralizers were installed on the casing to achieve optimum stand off along with a low friction factor which helped casing to run to the bottom successfully. A low rheology slurry tailored for optimum mechanical properties to withstand the fracturing operation was pumped and the cement returns to designed depth were noted. Cement bond log showed excellent results and the stage fracturing operation was performed with no issues with wellbore integrity. A tailored slurry and centralizer design helped to achieve zonal isolation objectives in the low clearance casing-in-casing (CiC) cementing configuration. The critical wellbore re-construction objectives were achieved, and the well was re-fractured with substantial increase in production.

Fibers are commonly used as lost circulation materials (LCMs) during cementing. Their evolution began with 2-in. long natural fibers, and glass fibers 3-mm long are now available to the industry to address lost-circulation issues. A major operator needed to cement 5-in. production liner in a depleted reservoir in the Gulf of Suez (GOS). The equivalent circulating density (ECD) exceeded the fracture gradient of the formation while circulating more than 1.5 bbl/min of mud. Losses were predicted during the cementing and an effective LCM added to the fluids was necessary to minimize the loss. A higher concentration of conventional fibers was not recommended because they can block the floats or area around liner-hanger slips. A new spacer and slurry design was formulated using two different types of LCM systems to help minimize losses during cementing. Both types have minimal chances of blocking restricted flow areas inside pipe. These LCMs help minimize risk of plugging floats or liner hangers, particularly in slim liners where the ID of float valves is only a couple of inches. Powdered LCM was used with the spacer only because it can affect cement slurry properties. This LCM can be used in at least two to three times higher concentrations than conventional fibers. The main objective of using it with spacer was to seal any loss zone before cement began entering into that zone. A different type of inert glass-fiber LCM was used with the cement slurry, but in lower concentrations, to provide extra safety measures for curing losses. The combination of these two fibers helped cure losses from a state of complete loss, to minor losses; later, no remedial jobs were required. This paper summarizes job design and lessons learned from this successful job, which can be applied globally, specifically for slim-liner jobs.

Underground gas storage (UGS) wells have emerged as a strategic solution in China. Success of UGS projects largely depends upon maintaining long term well integrity. Cement slurries that are placed across a wellbore should exhibit superior cement bonding as evidenced through a cement bond log (CBL) and long-term integrity to sustain the cyclic stress change by the injection and production process. Such slurries should have improved mechanical properties and the job execution should follow all cementing best practices. The well architecture included a 9 5/8-in. surface casing and a 7-in. production liner. The 7-in. Liner was run inside an 8.5-in. open hole and extended to surface using a tie-back liner. This well architecture should have a superior quality of cement across the entire liner. Multiple Finite Element Analysis (FEA) runs were performed to determine an optimum Young's modulus and Poisson Ratio for the cement slurry. These rigorous tests can take weeks to complete. As the well was shallow, to cover a wide range of well profiles, three different slurries were tested prior to the job. The initial mud weight planned for the well was in the range of 1.25 g/cm3 to 1.4 g/cm3. Due to gas influx, the mud density in the section was increased to 1.90 g/cm3. However, losses were also encountered at this mud density. Hydraulic modelling was revised, and slurry rheology and pumping rates were optimized to ensure equivalent circulation density (ECD) control within the pore pressure and fracture gradient window. Displacement rates were optimized to facilitate good displacement efficiency for hole cleaning. The slurry design was tailored with special additives to provide a synergetic effect of improving mechanical properties and minimizing seepage losses. Multiple computational fluid dynamics (CFD) runs were performed to evaluate the cementing job quality and based on the simulations it was decided to increase the cement volume to minimize any impact of contamination. The cementing job was performed with no operational issues and cement returns were observed above the top of the liner. Two different cement evaluation logs - CBL and ultra-sonic log, were conducted and showed good cement quality in the open hole section, meeting the well objectives. With this successful implementation, the tailored engineered cementing solution was highly recognized. The design and execution methodology were highlighted as the guideline for further successful cementing operations in UGS projects. This study shows a fully comprehensive and scientific way to improve cementing quality for long-term well integrity for UGS projects.