This paper presents the re-development strategy employed to recover attic oil from the highly-fractured crestal area of a carbonate reservoir. Optimum re-development strategies for the crestal area, along with planning and execution incorporating Best in Class (BiC) reservoir management practices are discussed.The crestal area was previously developed using full penetration vertical wells. After many years of continuous production and nearby injection, oil production rates in these crestal wells have declined with increasing water cut.The re-development strategy has been tailored to exploit this challenging opportunity and to maximize the production efficiently with selective placement of horizontal skimmer wells at the very top of the structure. Fit-for-purpose completion technologies were deployed to address the effects of the extensive fractures. Tapping oil continuously flowing into the crestal area by displacement, gravity, and capillary mechanisms, this re-development strategy has resulted in efficient and sustainable production.
Effective management of Voidage Replacement Ratio (VRR) throughout the producing life of an oil reservoir is essential for achieving optimal oil recovery. VRR is quantitatively defined as injection/production fluid volume ratio at reservoir conditions. The primary goal in managing voidage replacement is to replenish the energy in a reservoir to a degree that the producing wells yield hydrocarbons at economical rates. The determination of VRR, however, becomes more complicated when reservoirs are significantly affected by fluid influxes. This paper presents a method developed to optimize VRR calculations using streamlines, traced from finite-difference reservoir simulation model outputs. Good reservoir management practice necessitates that conventional VRR should be maintained at or above unity. Maintaining appropriate injection performance is therefore an essential requirement for achieving optimal oil recovery in secondary recovery processes. This can be achieved through effective VRR surveillance, water breakthrough monitoring, and reservoir pressure maintenance. This paper presents a new technique and associated workflow for rigorous VRR determination that resolves a number of shortcomings inherent in conventional VRR analysis. This rigorous VRRR determination methodology was applied to an existing field with considerable operating history including multiple displacement and recovery processes: primary depletion, aquifer influx, gas re-injection, gravity water injection, and power water injection. This new methodology utilizes finite difference reservoir simulation models to generate streamlines from the pressure field and fluxes. Streamlines represent flow paths between injectors and producers. The streamline trajectories with associated time-of-flight values thus obtained take into account geologic complexity, external fluxes, well locations, phase behavior, and reservoir flow behavior. Rigorous VRR estimates are obtained by accounting for the influxes and well allocation factors (WAF), which represent a measure of connectivity between specific injector/producer pairs with associated fluxes. The fluxes and WAF values are calculated automatically from the history-matched reservoir simulation model during streamline tracing for associated time steps. Traditionally, the well VRR values are calculated via the formulation of well inflow performance relationship (IPR), which may result in suboptimal estimations by not accounting for external sources of energy, such as influx from neighboring zones. The presented approach allows for improved optimisation of waterflood injection efficiency, where the off-set oil production can be derived directly from reservoir material balance (MB) calculations and streamline-generated well allocation factors. In order to facilitate VRR calculations with dynamic simulation regions, we propose a workflow for streamline (SLN) based VRR calculations using the time-dependent flow-based SLN-conditioned drainage volumes, automatically extracted from the simulation grid and iteratively incorporated into simulation model constraints as a function of simulation run time-steps.
Horizontal wells are increasingly being completed with inflow control devices (ICDs) in order to equalize the flow profiles, avoid water coning, enhance oil production, and minimize or eliminate downhole crossflow. Evaluating ICD completions is important to assess well performance, water entry intervals, completion efficiency, and potential remedial actions. Advanced multiphase production logging tools can be employed to evaluate the effectiveness of ICD completions. This paper examines case studies of two horizontal wells drilled along well trajectories with large heel-to-toe pressure differentials. These wells were drilled in a large carbonate reservoir with moderate fracturing in areas of high structural curvature, which added to the heterogeneity. Crossflow can occur under static and flowing conditions with sufficient contrast in reservoir pressure along the wellbore. Crossflow is undesirable especially when water enters the wellbore in one region and flows into the formation at another region, thereby reducing oil relative permeability in the latter region. This can adversely affect well performance and ultimate recovery. Advanced multiphase production logs and wellbore simulation are useful in the determining minimum well production rate required to avoid downhole crossflow. Multiphase production logging profiles were obtained for the two ICD-equipped horizontal wells in this study. These logs demonstrate the efficiency of ICD completions in minimizing crossflow when wells are produced above critical flow rates. However, the problem of crossflow remains when such wells are shut-in or produced at rates below their respective critical rates. These results show that comprehensive evaluation of wells exhibiting crossflow is necessary to minimize or mitigate crossflow and optimize well performance. Additional ICD design enhancements are recommended to control crossflow below the critical flow rate and to minimize undesirable gas/water production. Introduction Horizontal wells are commonly used in the oil industry to accelerate production and lower unit development cost. Horizontal well performance is affected by many factors, including reservoir heterogeneity, well placement and completion design. In heterogeneous reservoirs, the displacing fluid (water or gas) tends to move faster in zones with higher permeabilities, which will cause early breakthrough of unwanted fluids with eventual bypass of some undisplaced oil (Ouyang 2009). This can affect the pressure distribution and hence can cause crossflow between layers.
This paper presents the re-development strategy employed to recover attic oil from the highly-fractured crestal area of a carbonate reservoir. Optimum re-development strategies for the crestal area, along with planning and execution incorporating Best in Class (BiC) reservoir management practices are discussed.The crestal area was previously developed using full penetration vertical wells. After many years of continuous production and nearby injection, oil production rates in these crestal wells have declined with increasing water cut.The re-development strategy has been tailored to exploit this challenging opportunity and to maximize the production efficiently with selective placement of horizontal skimmer wells at the very top of the structure. Fit-for-purpose completion technologies were deployed to address the effects of the extensive fractures. Tapping oil continuously flowing into the crestal area by displacement, gravity, and capillary mechanisms, this re-development strategy has resulted in efficient and sustainable production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.