Review of studies on plugging compositions creation with controlled rheological properties and the ability to restore fluidity for completion, workover and abandonment of oil and gas wells

The main purpose of cementing oil and gas wells is zonal isolation of the formations exposed by the wellbore. During the entire life of the well, there should be no uncontrolled hydraulic communication between the developed formations and the surface, regardless of the composition and type of fluid (water, oil or gas). During the operation of the well, in addition to constant static ones, the casing and cement stone also experience various dynamic loads. The article presents an up-to-date review of experimental studies on the modification of grouting compositions and cement composites capable of autonomous selfhealing due to the introduction of various additives and nanomaterials. Such modification technologies significantly increase the tightness and resistance of cement to the effects of dynamic loads, the integrity of the cement stone. As a replacement for traditional cement materials, the authors propose the creation of grouting compositions with controlled physical and mechanical properties and the possibility of their re-liquefaction under the influence of temperature on the basis of bitumen or bitumen composites. Keywords: well plugging and abandoning; self-healing materials; autonomous self-healing; casing durability; impermeability of the cement stone; self-healing cement; bitumen and bitumen composites.

Double Casing Exit for Side-Track to Commingle Two Borehole Sizes Based Sections in One Slim Shot to Well TD

This project began when a 9-5/8" in 43.5 ppf production casing became inaccessible due to the existing cemented pipe inside, preventing further reservoir section exposure and necessitating a mechanical side-track meanwhile introducing the challenge of loosing one section and imposimg slim hole challenges. The size and weight of the double-casing made for challenging drilling, as did the eight very different formations, which were drilled. The side-track was accomplished in two steps, an 8½ in hole followed by a single long 6⅛ in section, rather than the three steps (16 in, 12¼ in, 8½ in) that are typically required. The optimal kick off point carfully located across the dual casing by running electromagnetic diagnostics, the casing collar locator, and the cement bond log. The double casing mill was carefully tailored to successfully accomplish the exit in one run. Moreover, an extra 26 ft. MD rathole was drilled, which helped to eliminate the mud motor elongation run. A rotary steerable system was utilized directly in a directional BHA to drill an 8½ in open hole building section from vertical to a 30⁰ inclination. A 7.0 in liner was then set to isolate weak zones at the equivalent depth of the outer casing (13-3/8"). Subsequently, a single 6⅛ in section was drilled to the well TD through the lower eight formations. Drilling a 6⅛ in section through eight formations came with a variety of challenges. These formations have different challenging behaviors relative to the wellbore pressure that typically leads to the drilling being done in two sections. Modeling the geo-mechanical characteristics of each formation allowed the determination of a mud weight range and rheology that would stabilize the wellbore through all eight formations. The slim, 6⅛ in, hole was stabilized with higher equivalent circulating density (ECD) values than is typically used in larger boreholes. Optimizing mud weight and drilling parameters, while managing differential sticking with close monitoring of real-time ECD, helped to stabilize the high-pressurized zones to deliver the well to the desired TD with a single borehole. This project represents the first time in Kuwait that double casings in such large sizes have been cut and sidetracked. It is also the first time these eight formations have been cut across such a smaller hole size, slim hole (6⅛ in) in a single shot. Geo-mechanical modeling allowed us to stabilize the pressurized formations and to control the ECD. The well also deployed the longest production liner in the field commingling multiple reservoirs with differnt pore pressure ramps, with excellent cement quality providing optimal zonal isolation.

Application of Wellbore Strengthening Techniques in Carbonate Formation Solves Lost Circulation Challenges During Liner Running and Cementing

For many years, the oil and gas industry has deployed techniques which enhance formation strength via the successful propping and plugging of induced fractures. Induced fracture sizes have been successfully treated using this method up to the 600 – 1,100-micron range. Static wellbore strengthening techniques are commonly deployed to cover 1,000 micron and all fracture size risks underneath. The deployment of wellbore strengthening techniques has historically been confined to permeable formations. In most cases, wellbore strengthening has been deployed to operationally challenging sand fracture gradients or, where boundaries are pushed, lower ranges of permeability, such as silts. The subject of wellbore strengthening in shales or carbonates to this day, remains a challenge for the industry, with very few documented success stories or evidence of sustained ability to enhance fracture gradient across a drilling campaign. This paper covers the history of lost circulation events which have been reported in the Khazzan/Ghazeer field in the carbonate Habshan formation. It also describes the design changes which were introduced to strengthen the rock and enable circulation/returns, during liner cementation. The design work built on experience applying wellbore strengthening techniques in carbonates in the Norwegian sector of the North Sea. This work is also summarized in this paper. The Habshan carbonate formation in Oman presents a lost circulation challenge through an ‘induced’ fracture risk. Since the beginning of the drilling campaign in the Khazzan/Ghazeer field, the Habshan formation has repeatedly experienced induced mud losses during well activities such as liner running, mud conditioning with liner on bottom and cementing, when the formation is exposed to higher pressures, less so during drilling. The Habshan challenge in Oman has led to regular, significant lost circulation events during cement placement, adding operational cost and more importantly, presenting difficulties around meeting zonal isolation objectives. Through previous field experience in Norway, a set of criteria was developed to qualify a standard pill approach to carbonate strengthening. The currently deployed strategy is designed to address both the risk of induced fracture by propping and plugging (wellbore strengthening) and provide some ability to seal natural fractures which are often encountered with carbonates, or similarly flawed rocks. The strategy deployed aims to cover these two risks with a blanket approach to lost circulation risk in carbonates. The success of this approach is demonstrated using well performance data from a total of 43 wells drilled before and after the introduction of the wellbore strengthening strategy. As it was initially assumed that wellbore strengthening could not be applied to carbonate formations, other techniques had been tried to prevent lost circulation. Those techniques provided mixed results. Since the implementation of wellbore strengthening significant improvements in achieving zonal isolation requirements and reducing fluid losses have been documented.

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.

Successful Deployment of Metal Expandable Technology with Inner String Stage Cementing System Overcomes Well Construction Challenges in Bab Field, UAE

Inability to effectively isolate depleted aquifer formations due to severe losses during cementation leads to accelerated corrosion of the production casing. Per current practice, a top job is performed from surface to fill the annulus with cement, but with limited success in a severe losses’ scenario. The objective is to improve zonal isolation by applying V0 rated multiple stage cementation technology with inner string thus enhancing well integrity during the life cycle of the well. A metal expandable annular sealing system was selected as a reliable isolation mechanism for effective cementation behind aquifers due to its ability to provide high expansion in potentially washed-out wellbores and the feature of long multi-element sealing systems with built in redundancy. The inner string operated stage cementing system provides a reliable solution to selectively and accurately place cement above the metal expandable packer whilst maintaining V0 casing integrity once closed. Additionally, the unique combination of technologies provides a cost-effective life of well solution compared to current stage cementing methodologies. Following successful execution of three trial jobs, the multi-stage cement using V0 rated tools and an inner string was compared to similar jobs done per current cementing practices. Analysis involved reviewing the cement bond column coverage and quality (CBL) with offset wells. Cement bond log results showed that this technique enhanced the cement column quality behind the 9 5/8" casing across the aquifer zones with moderate to good cement for the most part. Contaminated cement was observed just below the previous casing shoe and this could be addressed by adding another stage tool just above the previous casing shoe. Overall results show improved cement column quality for this section when compared to conventional jobs with similar conditions and is recommended for future use in severe to total losses scenario. In a situation where losses are seen at the previous casing shoe, a three-stage job is recommended. Other benefits include: Security and confidence in gas tight sealing capability and mechanical integrity Precise and conclusive operation for open, close and lock with no risk of accidental lock Ability to squeeze cement below the metal expandable packer No reduction in pressure rating regardless of OH ID and full bore ID of casing No post operation drill out required of the stage tools V0 stage cementing tools with inner string and metal expandable annular sealing system are not available on Oil & Gas market as a single tool. Therefore, this combined technology application of solutions from different technology providers to access a dedicated solution is totally novel and creates an opportunity for future applications across the industry.

Engineered Composite Lost Circulation Solution to Successfully Cure Total Losses During Drilling Across Naturally Fractured Formations in Ghawar Gas Field, Saudi Arabia

Lost circulation is one of the major challenges while drilling oil and gas wells across the world. It not only results in nonproductive time and additional costs, but also poses well control risk while drilling and can be detrimental to zonal isolation after the cementing operation. In Ghawar Gas field of Saudi Arabia, lost circulation across some naturally fractured formations is a key risk as it results in immediate drilling problems such as well control, formation pack-off and stuck pipe. In addition, it can lead to poor isolation of hydrocarbon-bearing zones that can result in sustained casing pressure over the life cycle of the well. A decision flowchart has been developed to combat losses across these natural fractures while drilling, but there is no single solution that has a high success rate in curing the losses and regaining returns. Multiple conventional lost circulation material pills, conventional cement plugs, diesel-oil-bentonite-cement slurries, gravel packs, and reactive pills have been tried on different wells, but the probability of curing the losses is quite low. The success with these methods has been sporadic and shown poor repeatability, so the need of an engineered approach to mitigate losses is imperative. An engineered composite lost-circulation solution was designed and pumped to regain the returns successfully after total losses across two different formations on a gas well in Ghawar field. Multiple types of lost-circulation material were tried on this well; however, all was lost to the naturally fractured carbonate formation. Therefore, a lost-circulation solution was proposed that included a fiber-based lost-circulation control (FBLC) pill, composed of a viscosifier, optimized solid package and engineered fiber system, followed by a thixotropic cement slurry. The approach was to pump these fluids in a fluid train so the FBLC pill formed a barrier at the face of the formation while the thixotropic cement slurry formed a rapid gel and quickly set after the placement to minimize the risk of losing all the fluids to the formation. Once this solution was executed, it helped to regain fluid returns successfully across one of the naturally fractured zones. Later, total losses were encountered again across a deeper loss zone that were also cured using this novel approach. The implementation of this lost-circulation system on two occasions in different formations has proven its applicability in different conditions and can be developed into a standard engineered approach for curing losses. It has greatly helped to build confidence with the client, as it contributed towards minimizing non-productive time, mitigated the risk of well control, and assisted in avoiding any remedial cementing operations that may have developed due to poor zonal isolation across certain critical flow zones.

Well Integrity Catastrophe Avoided Through Advanced Well Integrity and Reservoir Monitoring Analysis, a Case Study

Well integrity is one of the main challenges that are facing operators, finding the source of the well problem and isolating it before a catastrophic event occurs. This study demonstrates the power of integrating different reservoir monitoring and well integrity logs to evaluate well integrity, identify the underlying cause of the potential failure, and providing a potential corrective solution. Recently, some Injector/producer wells reported migration of injection fluids/gas into shallower sections, charging these formations and increasing the risk of compromised well integrity. Characterization of the well issues required integration of multi-detector pulsed-neutron, well integrity (multi finger caliper, multi-barrier corrosion, cement evaluation, and casing thickness measurements), high precision temperature logs and spectral noise logs. After data integration, detailed analysis was performed to specifically find the unique issues in each well and assess possible corrective actions. The integrated well integrity logs clearly showed different 9.625-inch and 13.375-inch casings leak points. The reservoir monitoring logs showed lateral and vertical gas and water movements across Wara, Tayarat, Rus, and Radhuma formations. Cement evaluation loges showed no primary cement behind the first barrier casing which was the root cause of the problem. Therefore, the proposed solution, was a cement squeeze. Post squeeze, re-logging occurred, validating zonal isolation and a return of a standard geothermal gradient across the Tayarat formation. Most importantly, the cement evaluation identified good bond from the squeeze point clear to surface, isolating all formations. All these wells were returned to service (injector/producer), daily annular pressure monitoring confirmed that no further pressure build up was seen. Kuwait Oil Company managed to avoid a catastrophic well integrity event on these wells and utilized the approach presented to take the proper corrective actions, and validate that the action taken resolved the initial well integrity issues. Consequently, the wells were returned to service, and the company avoided a costly high probability blowout.

Thermal EOR Conformance – A New Frontier for Asset Optimization: Steam Shutoff Pilot in Oman

Over the last 50 years, thermal EOR has been an effective method for reducing the viscosity of and recovering heavy oil from deep reservoirs. In mature thermal EOR projects, conformance is one of the main challenges for maximizing reserves and meeting long-term production expectations. In this paper, Occidental presents a novel pilot to address thermal conformance in the Mukhaizna field in Oman. This is a thermal EOR operation in deep reservoirs (> 2,000 ft) with extremely high viscosity (>10,000 cp) in harsh desert conditions with temperatures exceeding 500°F. The pilot area is a mature thermal area with 15 years of continuous steamflood operations. The novel conformance technique, based on a combination of chemical and zonal mechanical isolation systems, was developed in-house in a low oil price environment. The pilot area consists of multiple reservoir zones that have undergone vertical steam injection since 2005. Thermal conformance has emerged as a challenge because more than 60% of the injected steam has been preferentially entering the high-permeability zones, with only 40% of the steam entering the other zones, which hold a larger amount the remaining oil. The subsurface and well engineering teams collaborated to design a rigless operation using dual coiled tubing units, one for cooling water and one pumping a chemical gelation recipe that gels at a certain trigger gelation temperature at the target zone. Zonal isolation of the reservoir is achieved using a novel inflatable packer triggered mechanically by ball gravitation through coiled tubing at 500°F and retrieved after the temporary zonal isolation. The well and reservoir surveillance included gathering data for injectivity assessment, vertical injection logging, temperature profiles, tracer tests in offset producers, and well testing for determining water cut. The pilot improved vertical conformance, as injection logging showed 40% steam reduction was achieved in the target zone, and more steam was re-allocated to the shallow zones. In addition, there was a water cut reduction of more than 20% in offset producers, and oil production tripled over a period of 3 months, which paid back the cost of the pilot and generated positive cash flow. To our knowledge, based on an SPE literature search, this is the first successful thermal conformance operation conducted with the following combination of technologies: 1) Placing a novel chemical recipe through temporary zonal isolation with an inflatable packer, and 2) Using rigless operation of coiled tubing units at harsh conditions of >500°F and high pressure >1000 psi. The outcomes open a new frontier for thermal EOR development in multi-stack reservoirs, offering better utilization of steam injection and improving mobility control over the field life cycle. The cost of the pilot project was paid off in the first 6 weeks, and all chemicals used were developed in an eco-friendly system.

Value of Cement Bond Logs for Evaluation and Improvement of Cementing Practices in Extended Reach Drilling ERD Wells

This paper discusses the value of cement logs as the core input to analyze the cement quality and validate the improvements made to cementing designs and practices of the intermediate casing string in Extended-Reach Drilling (ERD) wells. The ERD wells are being drilled from artificial islands in a field offshore in the UAE. The primary cementing objectives are isolating the reservoirs from their sublayers and protecting the casing against possible future corrosion across an upper formation. Cementing challenges include higher angle deviation, higher mud weight requirements resulting from an anisotropic, unstable shale formation present above the reservoir section. Effective reservoir management requires sound zonal isolation to eliminate crossflow between different reservoir units. In combination with standard cement bond logs (CBL), ultrasonic technology has provided detailed information about cement quality and a qualitative indication of casing position in the borehole. These have also led to valuable insight into how continued cementing designs and practices improved zonal isolation. Improvements in cement quality seen as a result of enhanced casing centralization, optimized hydraulic model, modified cement rheology, displacement rate impact, among others, were confirmed with the cement log evaluation program. The paper will present the ultrasonic and standard CBL responses, which support the enhancements made to the cementing design and practices that yield the desired results. The cement quality has been improved in the ERD wells intermediate section through strategic modification in cementing practices. Cement evaluation logs have played a significant role in validating the cementing methods’ development. Consistently improved zonal isolation results have opened up the opportunity for future efficiency gains by eliminating routine CBL.

Cement Evaluation in Highly Laminated and Multi-Stacked Sandstone Reservoirs: The World First Novel Approach Using Dual-Physics Cement Bond Assessment

Advances in cement recipe, additives and cementing technology including light weight cement, ultra-low fluid loss cement blend and improved cement to mud rheology mixing to seal the continuous liquid channels have prompted the industry to find an innovative way to evaluate the cement bond and integrity with a more robust and integrated approach. Evaluating cement bond behind casing based on single tool platform had shown some inherent uncertainties mainly due to borehole effects, tool eccentralization and processing variation. This paper will highlight few case studies on the application of both electromagnetic acoustic wave (EMAT) and ultrasonic cement evaluation logs including the world's first tool combination in single run to enhance understanding on cement integrity and optimize the perforation interval for production. Channeling and microannulus occurrences whether dry or wet are the most common features in cement integrity evaluation and yet poorly characterized to prevent any unwanted cross-flow or adverse impact to production. Electromagnetic acoustic wave cement evaluation in combination with an ultrasonic tool allow direct quantification of compressional, shear and flexural attenuation properties of cement downhole as well as acoustic impedance and microdebonding feature of the cement. Separation between average shear and flexural attenuation curves may indicate presence of microannulus depending on the extent of the separation without any requirement of additional pressurized logging pass. Parameter threshold determination based on shear and flexural attenuation cross-plot also indicates severity of cement microdebonding. Results showed that good production rate with lower water cut and low GOR reading had been achieved from specific perforated zones in the well. Electromagnetic acoustic wave and ultrasonic cement evaluation tools had successfully defined the zonal isolation layers as thin as 2 to 3 meters along the wellbore and optimized the perforated zones to avoid any liquid channeling or premature water and gas breakthrough into the wells, which can affect the production attainability and drainage efficiency from particular reservoirs. In a nutshell, combination of EMAT acoustic wave and ultrasonic cement evaluation principles prove to provide a more comprehensive overview on the cement bond integrity behind the casing. Having two independent downhole measurement which complement each other will reinvent the effort in cement bond assessment for complex reservoir environment which is susceptible to interpretation ambiguity.