Successful Remediation of Sustained Casing Pressures in Gas Cap Injector Wells with the Use of Flexible and Self Healing System

Several injection wells in Prudhoe Bay, Alaska exhibit sustained casing pressure (SCP) between the production tubing and the inner casing. The diagnostics on these wells have shown communication due to issues with casing leaks. Conventional cement systems have historically been used in coiled-tubing-delivered squeeze jobs to repair the leaks. However, even when these squeeze jobs are executed successfully, there is no guarantee in the short or long term that the annular communication is repaired. Many of these injector wells develop SCP in the range of 300-400 psi post-repair. It has been observed that the SCP development can reoccur immediately after annulus communication repair, or months to years after an injector well is put back on injection. Once SCP is developed the well cannot be operated further. A new generation of cement system was used to overcome the remedial challenge presented in these injector wells. This document provides the successful application of a specialized adaptive cement system conveyed to the problematic zone with the advantage of using coiled tubing equipment for optimum delivery of the remedial treatment.

Engineered Solution Helps Tackle Tricky Shale Gas Cementing Challenge in HP/HT to Deliver Good Cement Bond Across Shale Section Located in Western India

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.

Rheological characteristics of the binder for foam concrete with a complex of mineral modifiers

The paper considers the effect of mineral additives on the rheological characteristics of a binder for foam concrete. The compositions in the study were divided into two groups: based on nanostructured binder (NB) and based on cement. For the compositions of the first group portland cement is proposed as a modifying additive,for the compositions of the second group NB and anhydrite were used as modifying additives. It has been shown that the introduction of cement into NB increases the viscosity due to an increase in the concentration of large-sized particles, while the combined use of nanostructured binder and anhydrite as modifiers of the cement system helps to reduce the viscosity of the cement mortar and increase its mobility, which reduces the amount of mixing water. From a technological point of view, this will make it possible to obtain materials with a rational pore structure by optimizing porosity processes.

Research and Application of Micro-Expansion and Anti-Channeling Cement Slurry System in Agadem Oilfield

The overall liner cementing qualification rate is only 40% in Agadem block of Niger, The cement slurry system used in the field has a UCA transition time of 43min, and an expansion rate of -0.03% in 24h, which result in a poor anti-gas channeling performance. The expansive agent and the anti-gas channeling toughening agent of anti-channeling agent were optimized through experiment study. A novel micro-expansion anti-gas channel cement slurry system which is suitable for Agadem block was obtained through experiment optimization study: 100% G +2 ∼ 4% fluid loss agent +3 ∼ 4.5% anti-channeling agent +1 ∼ 2% expansion agent-100S +0.15 ∼ 0.4% retarder +0 ∼ 0.3% dispersant +0 ∼ 0.25% defoamer + water. This new cement system has a good anti-gas channeling performance, the cement strength is 24.5-35.0MPa after 24hrs, the UCA transition time is 16-18min, and the expansion rate is 1.5-1.7%. At the same time, a cementing prepad fluid suitable for the block and the micro-expansion cement slurry system is selected to ensure the performance of the cement slurry's anti-channeling performance. The field test results proofs the good performance of the new cement system. The cementing qualification rate of Koulele W-5 well is 96%, and the second interface cementation is Good. The cementing qualification rate of Trakes CN-1 well is 100% which second interface cementation is Excellent. This paper has positive guidance and reference for cementing in Agadem block.

Successful Approach in Curing Lost Circulation in Depleted Aquifer Formations by Utilizing a Combination of Swelling Polymer & a Shear-Rate Rheology-Dependent Cement System; Case Study in UAE Land Operation

One of the greatest historically unsolved challenges to date in the United Arab Emirates is the failure to effectively cure the severe losses due to poor zonal isolation during drilling and cementing aquifer formations in particular the Dammam, UER & Simsima formations in the BAB field. Continuous efforts have been made to seek and pilot new technologies in UAE land operations to overcome drilling operation challenges, specifically chronic lost circulation in aquifer formations with the commitment to drive a more cost-effective operation and reduce the risk of Non-Productive Time (NPT). The current practice was not providing proper zonal isolation in the surface and intermediate sections. Most of the time aerated drilling was utilized while drilling the lost zones and conduct a top-up cement job to improve zonal isolation, but this results in limited reliability. It was necessary to identify a different approach to cure or significantly reduce the losses which would enable the hole section to be drilled successfully while minimizing operational risks, in a cost-effective manner. A technique combining two different technologies was selected: a swelling polymer lost-circulation material (LCM) that hydrates and helps reduce flow velocity into the formation, followed by a shear-rate rheology-dependent cement system. This cement system is a tunable and tailored slurry with thixotropic properties and has shown very cost-effective results with high success rates. It was then decided to tailor this approach to Abu Dhabi land operations to maximize wellbore asset value. After four subsequent trials targeting two different aquifer formations, the technique has shown tremendously promising results by successfully curing the losses providing above 80% returns. These combined technologies aim to eliminate or reduce effect of losses during cementing by performing the primary cementing job with complete returns or minor losses across aquifers thus enhancing wellbore integrity during the lifecycle of the well. It is hoped that this will eliminate, or at a minimum reduce production deferrals and subsequently improve plug and abandon (P&A) operations at end of field life. This paper aims to describe the challenges faced on the first three trials utilizing this technique and the solutions assigned for each trial based on the inputs, such as loss rate, formations interval exposed, design and lab testing for the pumped treatments as well as job execution details along with lesson learned for future jobs.

Effect of Nanocellulose in Cement Systems

Cellulose, the one of the most abundant biomaterials available in nature, is a polymer with cellobiose as the smallest repeating unit, with a degree of polymerization that can go up to 1000 for wood cellulose. The strength-to-weight ratio of nanocellulose is eight times greater than steel (Patchiya Phanthong et al). Nanocellulose in suspension (NCS) at a varied concentration helps increase properties of cement without changing the density of the cement slurry. Being mindful of challenges in oil and gas wells, efforts were made to enhance cement properties using nanocellulose within conventional and water-extended cement systems. Samples of 15.8-ppg conventional and 12 ppg water-extended cements were prepared by varying the proportion of nanocellulose within an aqueous suspension. Rheology, sedimentation, compressive strength and mechanical properties were analyzed for a conventional 15.8-ppg cement system with varying NCS proportions of 0, 2, 4, and 5% by weight of cement (BWOC). Similar work was performed for a 12 ppg water-extended cement system by varying NCS differently in proportions of 0, 5, 10, and 20% BWOC. Two-inch cubes were set at 170°F for 24 hours for each sample. They were crushed using hydraulic crush compressive strength equipment, and the force used to break the sample was recorded. Compressive strength for this cement system was measured to be 2450, 3250, 3450, and 3875 psi, respectively, for samples with 0, 2, 4, and 5% BWOC concentrations of NCS. An increase in the strength of cement with an increase in NCS percentage was observed for the 15.8-ppg slurry design, which may be attributed to the size and shape of the NCS. However, similar study carried out with 12 ppg water extended slurries showed decrease in overall compressive strength. Nano-sized particles fill the pores within the sample, impacting structural network development. Additionally, cellulose, having a fiber-like structure, may provide inter-particulate reinforcement. Based on the results of the 15.8-ppg cement system and the high tensile strength of nanocellulose, it can be determined that NCS has a positive effect for increasing mechanical properties. By applying nanocellulose, a tailored cement system (dependable barrier) can be designed to minimize risk and maximize production from oil and gas wells. Nanocellulose is of increasing interest for a range of applications relevant to the fields of material science and biomedical engineering because of its renewable nature, anisotropic shape, excellent mechanical properties, good biocompatibility, tailorable surface chemistry, and interesting optical properties. Low-volume NCS additions can alter the structure of the cured cement system and increase its mechanical properties. This reinforcing mechanism may provide a new opportunity for achieving higher strength cementitious materials.

Novel Resin-Cement Blend to Improve Well Integrity

A good primary cementing job governs in a great part the producing performance of a well. Successful zonal isolation, which is the main objective of any cementing job, primarily depends on the right cement design. The resin-based cement system, which is a relatively new technology within the oil industry has the potential to replace conventional cement in critical primary cementing applications. This paper describes the lab-testing and field deployment of the resin-based cement systems. The resin-based cement systems were deployed in those well sections where a potential high-pressure influx was expected. The resin-based cement system, which was placed as a tail slurry was designed to have better mechanical properties as compared to the conventional cement systems. The paper describes the process used to get the right resin-based cement slurry design and how its application was important to the success of the cementing jobs. The cement job was executed successfully and met all the zonal-isolation objectives. The resin-based cement's increased shear bond strength and better mechanical properties were deemed to be instrumental in providing a reliable barrier that would thwart any future issues arising due to sustained casing pressure (SCP). This paper describes the required lab-testing, lab-evaluation, and the successful field deployment of the resin-based cement systems.

Investigation of mineral hydraulic binders based on the slag-cement system obtained with the use of vortex electromagnetic homogenization

Из гранулированных доменных шлаков и портландцемента М500 с применением вихревой электромагнитной гомогенизации получены образцы минерального гидравлического вяжущего и искусственного камня на его основе. Исследованы физико-химические характеристики минеральных порошков: фазовый и химический состав, удельная поверхность, гранулометрический состав, механические свойства искусственного камня на основе вяжущих системы шлак‒цемент. Показано, что при введении в состав разрабатываемых материалов от 10 до 50 мас. % портландцемента предел прочности при сжатии образцов варьируется от 50 до 90 МПа, плотность ― от 2,1 до 2,5 г/см3. Данные материалы имеют низкую стоимость за счет использования доменного шлака в качестве сырья, а также благодаря применению энергоэффективной методики помола.

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

Magnesium oxysulfate (MOS) cement is a typical eco-friendly cementitious material, which presents excellent performances. In this work, a novel multiscale modeling strategy is proposed to simulate the hydration and pore structure of MOS cement system. This work collected and evaluated the Gibbs free energy of formation for main hydrates and equilibrium constant of main reactions in MOS cement system based on a first principle calculation using Material Studio. Followingly, the equilibrium phase compositions of MOS cement system were simulated through PHREEQC to investigate the molar ratio dependence of equilibrium phase compositions. Results showed that large M (MgO/MgSO4) was beneficial for the formation of 5Mg(OH)2·MgSO4·7H2O (Phase 517) and large H (H2O/MgSO4) tended to decompose MOS cement paste and cause leaching. The microstructure-based method visualized the hydration status of MOS cement systems at initial and ultimate stages via MATLAB and the results showed that large M was significant to reduce porosity, and similar results for the case of small H. Fractal analysis confirms that fractal dimension of pore structure (Df) was significantly decreased after the hydration of MOS and was positively correlated to the porosity of the paste. In addition, it can be referred that large M and small H were beneficial for modifying the microstructure of MOS paste by decreasing the value of Df.

Heavy Weight Cement System for Corrosive Environment: Preventing Strength Retrogression and H2S Corrosion

Well cementing in high temperature and hydrogen sulfide (H2S) corrosive environment presents challenges in preventing cement compressive strength retrogression and selecting weighting agents inert to H2S. This paper presents the development of a cementing system for high pressure high temperature (HPHT) well with bottom hole static temperature in excess of 165°C, a drilling fluid density of 2.19 SG and a high concentration of H2S. A major operator in the Caspian Sea region accepted the cement design and successfully used it on the production liner section of the HPHT well. Cementing of the production liner was complex due to the requirement for a high-density cement system, narrow margin between the pore pressure and frac gradient, HPHT conditions and 18% H2S concentration in the formation fluid. Comprehensive laboratory testing was performed to evaluate the properties of the cement system including measurements of thickening time and compressive strength evaluation using a UCA and destructive method using ultra-HPHT curing chamber for cube sample curing. The presence of H2S limited the use of conventional weighting agents such as hematite and hausmannite, and the high temperature environment dictated the need for quartz silica. These factors required a nonstandard approach to cement blend formulation and flowability assessment. During cement system optimization, the target slurry density was achieved using barite which has a lower density compared to other common weighting agents and significantly reduces cement content in the blend but also is inert to H2S corrosion. A further challenge encountered during cement system optimization was strength retrogression that could not be prevented by the conventional approach of adding 30-40% quartz silica by weight of cement into the system. To overcome strength retrogression, much higher concentrations of silica were required. As a result, the low cement content led to insufficient compressive strength development at liner hanger depth. A solution was found by adding a Vinylamide/Vinylsulfonated polymer (VA/VS) polymer in a certain proportion to the slurry design. Thus, at elevated temperatures, it was observed that the VA/VS polymer tended not to delay compressive strength development while still extending the slurry thickening time. The developed heavy weight cement system was successfully implemented to isolate the 7-in liner on HPHT well. All the stages of job planning, design and execution, along with the slurry optimization process are presented.