Summary A steam injection project was conducted in diatomite containing heavy, biodegraded oil (12°API, ?3,000 cp) in the South Belridge field, Kern County, California. The diatomite interval tested (the San Joaquin, Etchegoin, and Belridge diatomites) underlies an active steamflood in the sandstone of the Tulare formation. Initially, the test was to determine the viability of cyclic steam recovery from an unpropped, steam fractured completion in the diatomite. Four standard steam cycles were completed, with sluggish oil recovery [oil-steam ratios (OSR) were less than 0.1]. The well was then hydraulically fractured and propped. Two additional steam cycles were completed that had considerably greater oil recovery (OSR>0.2). The project was then configured for steamdrive by drilling a closely spaced producer. The new producer was initially completed with a propped hydraulic fracture and cycled once. The original cyclic producer was converted to continuous injection, and a two-well steamflood was operated for more than 1 year. During the steamflood, heavy oil was mobilized and response has been continuous. The configuration of the "pattern," with only one producer, results in poor capture efficiency. The performance of this incomplete pattern has been, as expected, poor (<0.1 OSR), but steam injection is shown to be a promising recovery technique for the heavy oil diatomite. The process is applicable to California diatomites, or any other high porosity, low permeability, shallow reservoirs that contain a significant concentration of heavy oil. Introduction It is estimated that the diatomite in the San Joaquin Valley of California contains as much as 10 billion barrels of oil. Mobil's former holdings in South Belridge, Lost Hills, and McKittrick, now part of Aera Energy, a joint venture between Mobil and Shell, contain on the order of 1 to 2 billion barrels. These formations are marked by high porosity (40 to 70%) and moderate to high oil saturation that can result in very high oil concentrations that are amenable to such recovery techniques as steam injection. The low permeability of diatomite (generally <1 md), however, makes any recovery technique very challenging. The diatomaceous facies of the Monterey formation is widespread along the western and central portion of the San Joaquin Valley and is one of the reservoir intervals for commercial production from the Lost Hills, South Belridge, McKittrick, Midway-Sunset, and Buena Vista fields. In some of these fields, such as South Belridge, productive diatomite reservoirs directly underlie highly productive massive steamflood operations in sandstones of the Tulare formation. These thick diatomite strata (up to 1,000 ft) form an attractive target and, in some respects, represent the final frontier for thermal recovery operations in onshore California. Especially attractive, if thermal operations can be utilized to unlock the diatomite, is the existing steamflood infrastructure available for the diatomite, particularly as conventional operations (such as the Tulare) decline sharply. South Belridge could certainly benefit from such a synergistic implementation. The South Belridge diatomite reservoir exhibits considerable areal and vertical variation in oil properties. In the central and southeastern portions of what were Mobil's properties, the upper portion of the diatomite reservoir contains heavy, biodegraded oil, the kind found in the overlying Tulare. Below this, the oil grades to intermediate and light. Further complicating the description is the mineralogy: the highly porous Opal A lies in the shallower depths, but has changed, due to increased temperature accompanying burial, from amorphous opaline silica to the less porous, more mechanically competent Opal CT. In South Belridge, Mobil had primary recovery operations for light oil in both the Opals A and CT, and waterflood operations in light (overlapping into the intermediate) oil in the Opal A. All wells for these operations are hydraulically fractured, a technique that opened the way in the late 1970's for accelerated development of the diatomite reservoirs in the San Joaquin Valley.1 Even so, the ultimate expected recovery is small (<20%, even for waterflood). Currently, Aera has no commercial operations in the heavy oil diatomite. Heavy and intermediate oil, at least for the former Mobil portion of South Belridge, represent a significant fraction of the total holdings. Commercial cyclic steam operations have been ongoing by Union, Chevron,2 and Texaco in the McKittrick field and pilot operations for cyclic and steamflood have been initiated by Cal Resources and Mobil (now combined as Aera Energy) in the South Belridge field.3–9 During the late 1980's, Mobil had several isolated field trials of cyclic steam injection in wells hydraulically fractured and propped in intervals containing either heavy or intermediate oil. These tests paved the way for our first intensive pilot to determine the feasibility of thermal operations in the heavy oil diatomite at South Belridge. Previous thermal pilots in the diatomite for heavy oil have utilized cyclic steam. The only previous pilot for steamflooding,3–9 also in the South Belridge, targeted a light oil interval. This pilot therefore represents the first cyclic steam followed by steamflooding for a heavy oil interval in the California diatomite. An additional area for concern to be addressed in this thermal pilot was how steam injection would affect the problematic subsidence in the diatomite10,11 and potential wellbore failures.12,13 Original Purposes of the Test. The initial purpose of the test was to determine the viability of high pressure steam injection into an unfractured interval of diatomite in the South Belridge containing heavy oil. The test had the following original objectives:quantify incremental oil production attributable to steam stimulation;better define the crude oil gravity and viscosity in the South Belridge diatomite;confirm the laboratory-based predictions of siliceous matrix dissolution and crude distillation resulting from steam injection;determine the feasibility of linkage to the natural fracture system; anddetermine the impact of steam cycling on localized formation compaction.
Ensuring long-term optimum completion performance is important for the economic development of any field. As fields are now developed with fewer wells and in more technically challenging environment, new technologies are required to provide guidance and quantify the impact of completion design. This paper presents a new methodology in coupling ExxonMobil's reservoir simulator and a detailed well hydraulics simulator that simulates reservoir, wellbore tubing and wellbore annulus flow simultaneously. Case studies indicate that unique completions opportunities in optimizing completions options, especially inflow control devices, are captured by using the modeling capabilities Completion strategies frequently include provisions tomaintain a uniform production profile along the wellbore,manage future risks (early water or gas breakthrough) and mitigate the potential for sand production, andimprove reservoir recovery. Completion options include open hole, cased hole, inflow regulation devices (inflow/flow control devices and inflow valves), sand screens, or pre-drilled liners. Different from nodal based wellbore simulation in a conventional reservoir simulator, the proposed coupled well and reservoir simulation provides not only detailed information on the tubing and annulus flow and associated pressure drops in and throughout all completion types, but also the impact of completions on short and long term reservoir flow and recovery. Studies have shown the importance in utilizing the coupled model in both history matching and model prediction when advanced completions are applied. The significance of this new coupled approach is its ability to capture both flow dynamics through various completion options and reservoir performance Introduction In the past, top performing fields produced thousands of barrels a day from each of dozen of wells with completions lengths spanning tens to hundreds of feet. Today, we are using far fewer wells, each producing tens-of-thousands of barrels a day, from much longer and more complex completions often spanning thousands of feet, and all of this in more technically challenging environments. Obtaining superior well performance requires both a better understanding of the physics that controls well production as well as new technologies that take advantage of physics-based knowledge. ExxonMobil develops unique, physics-based modeling capabilities that can be applied during well planning, design, and production to deliver optimized well performance over a well's life-cycle 1. Well completions are important means to optimize well performance throughout the entire well life, especially for challenging and remote environments. Commonly available completions options include open hole, cased hole perforated, slotted liner, inflow control devices (ICD), perforated liner, wire wrapped screen, gravel pack, frac pack, etc. For example, in ExxonMobil's Sakhalin-1 development, a combination of external isolation packers, inflow control devices, sand screens, and pre-drilled liners were used and the factors that were considered to configure the completions include rock strength, sand particle size, reservoir deliverability, reservoir description, etc.3 The challenging part from a completion design point of view is the understanding well inflow and outflow performance as a result of pressure drops due to multiphase flow in and throughout all completion types. More importantly, how the well inflow and outflow performance change over time. All these are the fundamentals for completion optimization - physics-based completion design, practices, and procedures for optimizing the selection, design, execution, and operations of wells in consideration of lifecycle risks and costs.
SPE Members Abstract Thermal reservoir simulation was utilized to understand, make development recommendations, and project the performance of the Monarch C steamflood in a portion of Mobil's South Midway Sunset field. The Monarch, a thick sequence of complex turbidite deposition, is characterized by extreme geological heterogeneity (lithofacies-controlled permeability and saturation variation, and mudstone barrier layers). Steamflood performance in the Monarch is related directly to the reservoir quality, and the path of steam flow is significantly influenced by the numerous laterally extensive mudstone barriers. The fine grain clay-bearing sediments were deposited on the anticline, distal from the source, whereas the coarser grain sediments, with little clay, were deposited on the more proximal syncline and steep dip areas. Consequently, steamflood performance improves relative to the crest since reservoir quality improves (including oil saturation), clay content decreases, and structure (dip) becomes more pronounced. The simulation models were constructed to capture the heterogeneity. Two models were constructed, a single pattern model for a pattern with good performance, and a multi-pattern strip model that linked patterns of good performance with poorly performing patterns on the crest of the structure. Simulation results indicated the initial completion strategy, that ignored the mudstone barriers, often resulted in misalignment between injector and producer completions that severely limited performance. A complete overhaul of the well completions was required to improve the steamflood. Subsequent to the simulation work, the steamflood was re-engineered, based on intensive pattern-by-pattern and well-by-well reviews, to include producer recompletions and limited entry steam injectors. Steamflood performance improved following the redesign. Introduction Mobil's MOCO 35 Fee Property in the South Midway Sunset field is located in Kern County, California. The Monarch, composed of four retrograding turbidite reservoir complexes (A, B1, B2, and C), offers an unusually complex geological environment for steamflood development. These sands were produced under primary and cyclic steam until an aggressive steamflood development plan was initiated in the mid-1980's for three of the reservoir complexes. A four-pattern pilot was started in 1986-87 (five-acre nine spots) and followed by further expansion in 1989-90. Steamflooding often includes a significant gravity drainage contribution, and therefore performance can be enhanced in reservoirs that have significant structure. In general structural terms, the Monarch sands consist of an anticline (present during deposition) that gently slopes into a syncline. Past the syncline, the sands have been greatly uplifted through Post-depositional folding resulting in a highly dipped structure ("steep dip"). The 12-pattern 1989 Expansion lies primarily on the top of the anticline, with the southern 3 patterns in the synclinal region. Figure 1 shows MOCO Section 34 and 35, the structural configuration, and the location of the pilot and the 1989 Expansion area. Subsequent development has moved west of the anticline, but has concentrated on the synclinal region and the highly productive steep dip area to the south and southwest. Figure 2 shows a schematic strike cross section for the three main sands of the Monarch: B1, B2, and C. Figure 3 shows a dip cross section for the same sands. P. 279
A steam injection project has been conducted in diatomite containing heavy, biodegraded oil (120 API, 3000 cp.) in the South Belridge field, Kern County, California. The diatomite interval tested (San Joaquin, Etchegoin, and Belridge diatomite) underlies an active steamflood in the sandstone of the Tulare Formation. Initially, the test was to determine the viability of cyclic steam recovery from an unpropped, steam fractured completion in the diatomite. Four standard steam cycles were completed, with sluggish oil recovery (Oil-Steam Ratios, or OSR's, are less than 0.1). The well was then hydraulically fractured and propped. Two additional steam cycles were completed, with considerably greater oil recovery (OSR's >0.2). The project was then configured for steamdrive by drilling a closely spaced producer. The new producer was initially completed with a propped hydraulic fracture and cycled once. The original cyclic producer was converted to continuous injection, and a two-well steamflood was operated for greater than one year. During the steamflood, heavy oil has been mobilized and response has been continuous. The configuration of the "pattern", with only one producer, results in poor capture efficiency. The performance of this incomplete pattern has been, as expected, poor (<0.1 OSR), but steam injection is shown to be a promising recovery technique for the heavy oil diatomite. Introduction It is estimated that the diatomite in the San Joaquin Valley of California contains as much as 10 billion barrels of oil. Mobil's holdings in South Belridge Lost Hills, and McKittrick contain in the range of 1–2 billion barrels. These formations are marked by high porosity (40–70%) and moderate to high oil saturation that can result in very high oil concentrations amenable to such recovery techniques as steam injection. The low permeability of diatomite (generally < 1 md), however, makes any recovery technique very challenging. The diatomaceous facies of the Monterey Formation is widespread along the western and central portion of the San Joaquin Valley and is one of the reservoir intervals for commercial production from the Lost Hills, South Belridge McKittrick, Midway-Sunset and Buena Vista fields. In some of these fields, such as South Belridge, productive diatomite reservoirs directly underlie highly productive massive steamflood operations in sandstones of the Tulare Formation by both majors and independents. These thick diatomite strata (up to 1000') form an attractive target, and in some respects, represent the final frontier for thermal recovery operations in onshore California. Especially attractive, if thermal operations can be utilized to unlock the diatomite, is the existing steamflood infrastructure available for the diatomite, particularly as conventional operations (such as the Tulare) decline steeply. Mobil's South Belridge could certainly benefit from such a synergistic implementation. Mobil's South Belridge diatomite reservoir exhibits considerable areal and vertical variation in oil properties. In the central and southeastern portions of Mobil's properties, the upper portion of the diatomite reservoir contains heavy, biodegraded oil, as is found in the overlying Tulare. Below this, the oil grades to intermediate and light. Further complicating the description is the mineralogy: the highly porous Opal A lies in the shallower depths, but has changed, due to increased temperature accompanying burial, from amorphous opaline silica to the less porous, more mechanically competent Opal CT. In South Belridge, Mobil has primary recovery operations for light oil in both the Opal A and CT, and waterflood operations in light (overlapping into the intermediate) oil in the Opal A. All wells for these operations are hydraulically fractured, a technique that opened the way in the late 1970's for accelerated development of the diatomite reservoirs in the San Joaquin Valley. Even so, the ultimate expected recovery is small (<20%, even for waterflood). Currently, Mobil has no commercial operations in the heavy oil diatomite. Heavy and intermediate oil, at least for Mobil's South Belridge, represent a significant fraction of the total holdings. Commercial cyclic steam operations have been ongoing by Union, Chevron, and Texaco in the McKittrick field and pilot operations for cyclic and steamflood have been initiated by Cal Resources and Mobil in the South Belridge field. P. 403^
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.