TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe widespread use of FracPack technology in deepwater reservoir has been a growing practice. Its purpose is sand control and well stimulation. To-date, field applications and fracture treatments have been designed using traditional hydraulic fracturing simulators that apply LEFM theories. While this is adequate for hard rocks (e.g., tight gas formations), the fracture geometry predictions fall short when applied to fracturing soft rocks. Soft rocks are normally at incipient plasticity and, hence, are prone to compaction.Compaction, or plastic rock deformations during sand control FracPacks operations and disposal of drilling cuttings slurries in soft layers. The capacity of the created fracture to store or accept solids, the conditions of the rock strength near the fracture faces and the near well/fracture rock porosity or permeability are all highly impacted by the rock compaction during the fracture propagation process.
Drilling waste disposal through downhole hydraulic fracturing is often the preferred waste management option because it can achieve green operation and often has favorable economics. Most field situation comprise of injection in either dedicated well or in the annulus of an existing well. Containment of the disposed waste must be ensured and one of the questions in drilling waste injection operations is what the capacity of a disposal well or annular scheme is? The answer to this question depends on downhole waste storage mechanisms. It is evident from laboratory simulation studies and field operation experience that multiple fractures are created in drill cuttings injection (DCI) operations and the capacity of a disposal well is much larger than that estimated from single fracture simulations. More importantly, as more solids are injected into the disposal formation, the local stress is modified. Because of this change in local stress, fracture shapes and extents at the beginning of a DCI operation can be significantly different from the fracture shapes and extents at the end the operation. Modeling of this fracturing evolution process is necessary and essential to ensure the safe containment of the disposed waste and to estimate accurately the disposal capacity of a drilling waste disposal well. This paper presents a numerical algorithm for modeling the multiple fracturing and fracture evolution process during drill cuttings injection operations. Case studies show that the modeling results based on multiple fracturing have significant impacts on DCI operations engineering such as injection pressure requirement and disposal capacity. The results also provide insight into best practices for the containment of disposed waste, when injection can continue into a previous zone and when is there a need to inject into a different zone or when a new disposal well should be drilled. For the purpose of brevity, "disposal well" will be used to designate either a dedicated injector well or an annular injection scheme. Introduction Figure 1 shows an overview of a drill cuttings injection (DCI) scheme. Briefly, a drill cuttings injection operation involves collection and transportation of solid waste from control equipment on the rig to a slurrification unit, where the cuttings are ground (if needed) to small particles in the presence of water to make a slurry. The slurry is then transferred to a slurry holding tank for final slurry rheology conditioning. The conditioned slurry is pumped through a casing annulus or a tubular into sub-surface fractures created by injecting the slurry under high pressure into the disposal formation. The waste slurry is often injected intermittently in batches into the disposal horizon. The batch process consists of injection of roughly the same volumes of slurry and shutting-in the well after each injection. This allows the disposal fracture to close onto the cuttings and to dissipate any build-up of pressure in the disposal formation. This fracture closure and local fracture closure pressure increase due to the presence of the injected solids promote new fracture creation from next batch injection. The new batch fracture will not be aligned with the azimuths of previous existing fractures. Each batch injection may last from a few hours to several days or even longer, depending upon the batch volume and the injection rate.
Summary Key factors in framing a produced water management (PWM) strategy include a company's internal and external environments, technology, and business drivers. Emerging trends for establishing an environment-friendly PWM position comprise adoption of these policies:Move toward zero emissions.No discharge to surface or seas.Waste-to-value conversion.Incremental and progressive separation.Proactive efforts to influence partners, regulators, and environmental laws. This paper covers technical approaches for addressing the production, separation, and disposal/injection segments of water injection and reservoir waterflooding procedures and the basis for selecting strategy components and PWM actions. Best practices result both from comprehensive assessments of current PWM tools and from the insights obtained from a decade-long joint industry project (JIP) on produced water re-injection (PWRI). PWRI for waterflooding or disposal is an important strategy for deriving value from waste while preserving environmental integrity during exploration and production (E&P) operations. Advances in best practices and lessons learned for injector design, operation, monitoring, assessment, and intervention provide the basis for cost minimization and green operations. Facility and subsurface engineering are linked through PWM quality targets, pumping needs, injector completions, and facility constraints. Field cases and data mining results (Abou-Sayed et al.2005) show the variation in injector responses and underline the key elements contributing to performance. Field evidence indicates that injectivities suffer in matrix injection schemes despite the injection of clean water. Alternatively, injectivity maintenance using untreated produced water is feasible. The majority of injectors fracture during injection, thereby impacting facilities' statement of requirement (SOR), injector completion, sweep, and vertical conformance. This paper assesses fracture propagation during seawater and produced water injection and its impact on injector performance. Models depicting plugging of formations and fractures, vertical water partitioning, and well testing are discussed. Best practices are highlighted and the impacts on injection strategy outlined. Several field cases, as well as water injection design and analysis tools for quantifying the impact on flood and well performance, are presented. Introduction PWRI technology application for oilfield management has been steadily increasing over the last decade in various parts of the world (Sirilumpen and Meyer 2002; Van den Hoek et al.2002; Furtado et al. 2005; Hjelmas et al. 1996). Successful injection operations have been reported by operators in the North Slope of Alaska, the west coast of Africa, and the North Sea. PWRI offers the dual benefit of disposal of oil-filled waste water and solids in an environmentally safe way and enhanced hydrocarbon recovery by improving reservoir fluid sweep and pressure maintenance. The successful application of this technology in the oil field does not depend only on the disposal of solids/contaminants, but also on the maintenance of injectivity for effective sweep and injection conformance for improved recovery. This paper discusses the physical phenomena, namely matrix and fractured injection, involved in PWRI and the associated issues with regard to injectivity and facility requirements. A fracture plugging and propagation model is presented to explain the cyclic injection pressure behavior observed in some injectors. Thermal fracturing can allow fracture containment and reduce injection system requirements. Field cases clearly showing the effect of injection water temperature on fracture pressure and injectivity are discussed. The knowledge gained from the JIP is used to establish guidelines and best practices for implementing a PWM strategy.
The majority of injectors are likely to be fractured (intentionally or unintentionally) during their life cycles. Assessment of facture conductivity damage and associated surrounding formation damage is an essential step for maximizing and maintaining injector performance during produced water injection for water flooding. Fractured injectors experience less injectivity decline over time in comparison to matrix injectors. The current paper will present a mechanistic model for the plugged fracture behavior and discuss its applications to field cases. In addition, implications, recommendations and best practices for optimized produced water injection will be addressed within this context. The well undergoes two distinct processes that alternate over its life to create the sustained injectivity behavior associated with this scheme. Injectivity damage can occur particularly in pseudo-matrix conditions, where a stationary fracture progressively plugs (in addition to permeability impairment of the surrounding reservoir rock), resulting in pressure buildup and injectivity decline. As solids are deposited in the fracture, the "effective" exposed surface area is gradually reduced, at least partially, as a function of the injected amount of solids.Furthermore, fracture face damage (external filter cake build-up) and accumulated surrounding formation damage (internal filter cake build-up) progress as the volume of injected water increases. This plugging process continues until the injection pressure required for the designated injection rate reaches a critical value, which is greater than the pressure required to re-fracture the formation and/or to extend or propagate the plugged fracture. At such pressure a sudden fracture propagation or further breakdown of the formation is evidenced by a sudden increase in the Injectivity Index or similarly, a sudden drop in the Reciprocal Injectivity Index - RII - (unit injection pressure per unit constant injection rate).Thereafter, the required pumping pressure drops and/or the injection rate increases with the newly created surface area that has been caused by fracture propagation or initiation.The process then repeats itself. As the pressure rises it approaches and finally exceeds the fracture pressure required for further propagation, resulting in a saw-toothed shape pressure-time (or rate-time) behavior. The slopes of the bounding lines are controlled by the damaged formation and fracture characteristics, as well as the injected water quality.The slopes can be made to diverge, converge or remain almost parallel. The third option indicates a well optimized injection scheme. The final section of this paper will imply lessons learned, mitigation strategies, conclusions and recommendations based on analyses of field data from a number of produced water injectors. Pressure transient analysis and results from pressure fall-off test will be presented to verify the study results. Introduction Practices in the oil and gas industry have had to adapt with stricter environmental laws and regulations. Produced Water (PW) management is one of the main operating standards that have been affected by these changes. The safe, environmentally friendly and economical handling of PW is an essential ingredient in the success of any operator. Fortunately, PW liability can be coverted into an asset through injection during waterflood operations, provided the operator can successfully manage the main concerns. Produced Water Re-Injection (PWRI) can meet both waterflooding and pressure maintenance requirements. Concerns regarding PWRI fall under two categories. First, is the water going where it is supposed to (i.e., profile conformance)? Second, can the desired injection rate be met, both in the short and long term (i.e., injectivity maintenance)? By assuring these two key issues, a successful injection project can be executed. Tracking PW injector's performance is required for assurance.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMany of the largest fields yet to be developed around the world contain oil, water, and high concentrations of sour gas.
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