Gumarov, Salamat (Schlumberger) | Benelkadi, Said (Schlumberger) | Bianco, Eduardo (Schlumberger) | Woolf, Shaun (Schlumberger) | Hardy, Chris (Schlumberger) | Ido, Hisataka (ADOC Japan) | Tanaka, Manabu (ADOC Japan) | Tominaga, Naohiro (ADOC Japan) | Yahata, Kazuhiro (ADOC Japan) | Okuzawa, Taker (ADOC Japan)
Management of drilling wastes presents major challenges during drilling operations in environmentally protected areas. An Abu Dhabi offshore field development project selected cuttings reinjection (CRI) services as an appropriate solution for waste management.
Although CRI is a proven technology in the region, fracturing injection always inherits its own containment-related risks. To prevent all possible failures that were experienced earlier in the industry globally, a novel real-time monitoring and analysis of fracturing injections data was introduced.
A comprehensive front-end engineering design (FEED) study was performed to evaluate the feasibility of CRI techniques by selecting a suitable injection formation and designing a CRI-dedicated well, surface facilities, slurry testing, and appropriate operations execution plan.
The CRI well was drilled and completed to accommodate waste volumes. An assurance program based on industry best practices was used to support zero solids settling, fracture, or perforation plugging.
To achieve on-time intervention, the first real-time CRI data transfer through a satellite-based network to a support center staffed by global experts in Abu Dhabi was deployed to analyze fracture injection and shut-in pressure responses for early identification of possible risks and to map the fracture waste domain.
The project has been operated successfully since its inception with more than 300,000 bbl of drilled cuttings and drilling waste fluids injected since July 2016. No injectivity issues were experienced during drilling waste fluids injection. Several on-time interventions had been made to prevent well plugging and to maintain surface injection pressures within normal ranges.
Real-time data streaming has made a step-change improvement in the data delivery process, monitoring, and fracture pressure analysis. It creates a direct link between the wellsite and worldwide multidisciplinary technical expertise centralized in Abu Dhabi and provides visualization capability at any time and to any where to all personnel involved in the project.
This step change in monitoring CRI operations provides an acquisition-to-answer" integrated solution, mitigates the injection risks, and enhances the intrinsic value of CRI services.
The paper shares the experience of implementing the novel real-time CRI subsurface injection assurance program dedicated for cuttings reinjection operations. Real-time support from multidisciplinary experts provides live injection monitoring and fracture waste domain mapping for highly complex and risk-prone subsurface injection environments with stringent regulations
Haddad, Mohamed (ADNOC Offshore) | Rashed Al-Aleeli, Ahmed (ADNOC Offshore) | Toki, Takahiro (ADNOC Offshore) | Pratap Narayan Singh, Rudra (ADNOC Offshore) | Gumarov, Salamat (Schlumberger) | Benelkadi, Said (Schlumberger) | Bianco, Eduardo (Schlumberger) | Mitchel, Craig (Schlumberger) | Burton, Phil (Schlumberger)
Injection of drilling waste into subsurface formations proves to be an environmentally-friendly and cost-effective waste management method that complies with zero discharge requirements. It has now become the technology of choice in offshore Abu Dhabi.
The aim of cuttings reinjection (CRI) is to mitigate risks associated with subsurface waste injection and reduce cuttings processing time and cost. In order to meet these goals, a cuttings reinjection subsurface assurance methodology was developed to improve cuttings processing and continuously monitor drilling waste injection operations.
Preparing for CRI operations required extensive drilling cuttings slurry testing to minimize processing time and develop optimum particle size distribution to reduce cost and increase the injected waste volume. The improvements were accompanied by downhole pressure and temperature monitoring of the injection well, thus facilitating analysis of injection pressures. Fracture containment was verified through a combination of pressure decline analysis, periodic injectivity test, temperature survey, and periodic modelling for fracture waste domain mapping. A backup injection well was used also as an observation well to monitor the pressure signitures in the injection formation.
More than 1 million barrels of drill cuttings and associated drilling waste have been safely and successfully disposed of into a single injection zone of CRI well over three years of operations.
The cuttings reinjection subsurface assurance method optimizes grinded cuttings particle size distribution, detects and identifies potential risks to provide mitigation options to prolong the life of the injector.
The proactive subsurface injection monitoring-assurance program was built into the fit for purpose CRI injection procedure to continually avoid injecting any rejected hard material, improve and update the process as per subsurface injection pressure responses, thus reducing processing time and cost, mitigating injection risks, and extending the injection well life.
This paper presents the unique and technically challenging cuttings slurry properties design and pressure interpretation experience learned in this project; the enhancement of cuttings processing helped increase injection volumes and an in-depth interpretation of fracture behavior which behaved like a risk-prevention tool with mitigation options. Significant enhancement was developed in slurry treatment procedures to avoid injectivity loss and maximize the disposal capacity.
Mehtar, Mohammed (Abu Dhabi Marine Operating Company) | Haddad, Mohamed (Abu Dhabi Marine Operating Company) | Toki, Takahiro (Abu Dhabi Marine Operating Company) | Gumarov, Salamat (M-I SWACO, a Schlumberger Company) | Benelkadi, Said (M-I SWACO, a Schlumberger Company) | Shokanov, Talgat (M-I SWACO, a Schlumberger Company) | Vizzini, Carla (M-I SWACO, a Schlumberger Company) | Mitchell, Craig (M-I SWACO, a Schlumberger Company) | Khudorozhkov, Pavel (M-I SWACO, a Schlumberger Company)
This paper examines the challenges, solutions and milestones of the hydraulic fracturing based cuttings reinjection (CRI) process implemented on two artificial islands offshore Abu Dhabi.
During the development of an offshore field from two artificial islands, disposing of vast amounts of drilling waste and cuttings, generated from almost 100 wells, presented a major challenge. The conventional skip-and-ship for onshore treatment and disposal was technically, logistically, and economically unviable and posed possible future environmental liability. After careful assessment, total containment of drilling waste on the islands through multiple hydraulic fractures in suitable formations, for permanent in-situ waste confinement, was concluded by the operator as environmentally and economically the only sustainable process.
Two CRI wells were planned on each island to accommodate an estimated 8 million barrels of drilling waste slurry expected to be generated at the islands. While CRI is a proven technology wherein cuttings are slurrified and injected into sub-surface formations, fracture injections have high risks too. Many failures are known in the industry, including well and formation plugging and waste breaches to sea-bed and near-by wells, with far-reaching consequences and liability to operators.
Considering the complexity of the multiple-hydraulic fracturing process that requires careful planning, execution, monitoring, and analysis, a comprehensive geomechanical study was performed to identify and characterize all potential injection formations to achieve successful long-term injection. This was followed by front-end engineering design (FEED), fracture simulations, CRI well design, surface facilities design, slurry simulations, and followed by careful execution.
Two CRI wells were drilled on each island. Specifically designed injectivity tests were performed on each well before commencing injection, followed by regular injectivity tests to continuously analyze fracture behavior. A carefully designed slurrification and injection process, incorporating detailed QA-QC at all process stages, was implemented that helped to avoid solids settling, fracture or perforation plugging, uncontrolled fracture propagation, or well integrity issues. About 500,000 barrels has been successfully injected to-date in two CRI wells with injection pressures as per FEED estimates.
The paper details also the proactive sub-surface injection monitoring-assurance program built into the CRI injection procedure to continually modify the process as per sub-surface pressure responses, thus proactively mitigating injection risks.
Periodical injectivity tests, model alignment studies, temperature logs, and fracture pressure analysis facilitated regular recalibration of the geomechanical model to define fracture-domain sizes, monitor fracture height growth, and estimate residual formation domain capacity as injection progressed.
The multiple-hydraulic fracture-based CRI process implemented first time in Abu Dhabi incorporates many unique features which can be applied in similar projects elsewhere. This paper also describes the downhole gauges for accurate pressure-temperature monitoring at perforations, a detailed slurry design, the particle-size distribution for slurry quality analysis and quality control, the sub-surface monitoring-assurance program and regular tests and recalibration studies.
During the past decade, waste injection (WI) technology, also known as cuttings re-injection (CRI) technology, has been gradually accepted as an environmentally-friendly and cost-effective ultimate disposal method for drilling-related solids and liquid materials. In waste-injection operations, waste slurry is usually intermittently batch injected into appropriately selected subsurface formations. These slurry injections cause injection pressure and in-situ stress to gradually increase as more and more injected solid tends to accumulate in the near-wellbore fracture domain area. Moreover, solids in the leftover slurry can settle out and plug the wellbore during shut-in periods. These issues challenge injection equipments, wellbore integrity, waste domain containment and disposal capacity, and may hinder or terminate injection operations unexpectedly. Therefore, slurry must be properly overflushed from the wellbore and near-wellbore fracture area effectively and immediately. Effective execution and engineering analysis of post-slurry overflushing have become keys for successfully maintaining critical injection assets. A vigilant monitoring of surface, downhole tubing and annulus pressures makes these analyses possible in a timely and proactive manner.
In this paper, post-slurry overflushing with viscous pill and solids-free seawater is numerically modeled for analyzing efficiency of the overflushing and the effects of volume and rheology of the pill on the overflushing in a waste injection well. Moreover, the continuous pressure monitoring in two waste-injection projects in two offshore oilfields provides long-term downhole pressure data. These data were collected and analyzed for instantaneous shut-in pressure (ISIP) after each slurry injection and each post-slurry overflushing, and he effect on in-situ minimum stress and injection pressure was analyzed by comparing ISIP changes before and after overflushing. The studies on ISIP changes confirm the results of the numerical modeling in this paper.
Field studies and modeling results also show that overflushing with the appropriate rheologically-designed viscous pill/seawater sequence can decrease long-term injection pressure buildup rate, avoid wellbore/fracturing plugging and extend ultimate disposal capacity.
Drilling waste sub-surface disposal, via injecting into a pre-defined suitable formation, known as Waste Injection (WI) technology; has been selected as a primary drilling waste management tool for the development of a major oil field in the Caspian Sea. The field development has been utilizing WI technology since the beginning of development drilling operations. The main drivers were proven track record of the technology, meeting "zero-discharge?? environmental requirements and elimination of logistical complications associated with onshore transfer of drill cuttings. A dedicated WI well was drilled and the surface equipment package to process and inject drilling waste was installed on each drilling and production platform.
WI failure was considered as one of the top ten risks to achieving full field production targets. Complexity of the injection horizon consisting mostly of massive mudstone, regional faulting and tectonic activity combined with a lack of local WI experience called for a detailed sub-surface engineering design and meticulous monitoring of the waste disposal domain.
Continuous pressure monitoring was recognized as a critical approach in providing sub-surface assurance and timely identification of any early-warning signatures. Unique to these WI wells, the injection wells were equipped with down-hole pressure-temperature gauges for accurate pressure measurement and subsequent analysis.
This paper discusses the execution, results and conclusions of monitoring this challenging project over a 5-year period, including subsurface complexities experienced during this period such as very high injection pressures, limited fracture-wellbore communication, enhanced solids settling, observation and explanation of long-term pressure trend behaviours. In addition solutions developed to prolong the life of the injection asset; including enhanced seawater "over-flush?? injection strategy coupled with down-hole pressure measurement, careful monitoring and analysis.
The subsurface injection of drilling waste has become an increasingly popular and well-accepted technology over the last several decades. The popularity of this technology is primary spurred by its economic advantages in meeting more stringent drilling waste management requirements, especially in remote and environmentally sensitive areas. Furthermore, its use has become more attractive with the dramatic development and improvement in the processes associated with surface and sub-surface engineering, fracture modeling, risks identification and mitigation options, injection monitoring and in-depth pressure analysis. Together, these advancements have improved considerably the assurance and efficiency of waste injection operations worldwide.
Nevertheless, despite the tremendous advancements in the fracture modeling attained from subsurface feasibility studies, a major uncertainty exists with the propagation of multiple-fractures that apparently accompanies the intermittent batch injection process, essential to the drilling waste injection operation. The propagation of multiple-fractures, along with their orientation and complexities, strongly influence the fracture design, ultimate disposal capacity and injection pressure behavior. Consequently, this uncertainty is a critical issue, both in drilling waste injection and re-fracturing in conventional stimulation treatments.
This paper describes the evolution of understanding of multiple-fracture mechanics in drilling waste injection, starting from the conventional "wagon-wheel?? uniform disposal-domain concept to the branching multiple-fractures approach that becomes practical through mathematical computations of near-wellbore changes in the stresses resulting from prior fracture creation and solids accumulation. Moreover, the authors present four potential scenarios of subsequent fracture initiation and propagation during intermittent injections, and provide revised re-assessment of data from the joint industry Mounds Drill Cuttings Injection Field Experiment.
Waste Injection Background
Major technologies developments have occurred since the first hydraulic fracturing stimulation job was conducted in 1947 on the Kelpper Well 1. In that pioneering well, about 24 bbl of fluid were pumped into a limestone formation of the gas reservoir to treat each of the four pay zones. Today, research and resultant technology advancements permit immense hydraulic fracturing stimulation jobs comprising huge volumes of fluid to produce very-low permeability hydrocarbon reservoirs economically. These technological advancements also have opened the door for applications other than production stimulation. The injection of drilling wastes has evolved as one of those alternative applications. Waste Injection (WI), however, differs from a production stimulation operation in many ways.
The injection of drilling generated waste into a selected subsurface formation has evolved into the most preferred waste disposal technology in terms of environmental compatibility and cost effectiveness, especially for remote and environmentally sensitive areas. The main principle of waste injection (WI) is the initiation of hydraulic fracture and the placement of solids within the created fractures through the high-pressure pumping of slurry batches. The fracture propagation is governed mainly by in-situ stresses. As injection progresses solids accumulation in the fracture leads to an increase of in-situ stresses within the injection zone causing a build-up of injection pressure. As allowable injection pressure is often limited by equipment, the undesirable or rapid injection pressure build-up could jeopardize the operational life of an injection well and limit its waste disposal capacity.
This paper introduces a new approach to a regular seawater injection by investigating the relationship between pressure behavior and seawater injection. Displacement of slurry from the tubing by seawater over flush is carried out routinely in WI operations worldwide. However, never before it was considered as a pressure maintenance tool. The authors describe the impact of continuous seawater injection on injection pressure through the lifetime of three waste injectors. The injection pressure behavior before, during and after continuous seawater injection was reviewed using downhole measured data. It was noticed that regular seawater over-displacements during the continuous time periods between slurry injections reduced injection pressure considerably. Consequently, a thorough evaluation was initiated to investigate the impact of extended seawater injection on in-situ stresses and its potential advantage in maintaining the injection pressure within lower limits.
Considering the novelty and value of study for expanding worldwide WI operations, this paper presents the new approach to seawater injection as an injection pressure and disposal capacity maintenance tool.