The First Eocene is a multi-billion-barrel heavy oil carbonate reservoir in the Wafra field, located in the Partitioned Zone (PZ) between Kingdom of Saudi Arabia and Kuwait. After more than 60 years of primary production, the expected recovery is low and provides a good target for enhanced oil recovery (EOR) processes. A phased piloting approach has been used to reduce the uncertainties (subsurface and surface) related to application of thermal EOR processes in this field. This paper outlines the motivation for and benefits of the phased approach leading to steamflood development in the First Eocene reservoir. The key learnings from each phase, with focus on the progress made in identifying and mitigating key uncertainties for carbonate steamflooding, are discussed in detail.
The first step of the phased approach was an extensive EOR screening study in 1996 that identified steam flooding as a viable EOR process for this reservoir. In 1999, the Eocene Steam Stimulation Pilot, a multi-well cyclic steam stimulation (CSS) test, was conducted to provide information regarding the applicability of steam injection to Eocene reservoirs. The pilot evaluated reservoir, production and operational factors associated with injecting steam into the First Eocene reservoir. This was followed in 2005 by single 5-spot pattern pilot known as the Small-Scale Test (SST). The primary objectives of the SST were to address uncertainties regarding steam injectivity and the ability to generate steam from Eocene produced water. The SST successfully proved sustained injectivity in the dolomite reservoir using steam generated from produced water. The SST was followed in 2008 by a 16-pattern pilot referred to as the Large-Scale Pilot (LSP). The LSP was designed to evaluate the technical and operational feasibility of continuous steam flooding and further reduce 1) subsurface uncertainties such as recovery, vertical (potential barriers and baffles)/horizontal (high permeability layers or streaks) heterogeneity, steam-rock/steam-water interactions, and, 2) operational uncertainties associated with scaling and corrosion.
Key objectives of each pilot were defined and phase-appropriate subsurface/engineering design, reservoir surveillance and subsurface response plans (linked to the uncertainty management plan) were formulated to meet pilot objectives. Detailed data analysis (logs, cores, production, pressure, temperature, fluid properties, geochemical), reservoir characterization (stratigraphy, petrophysics, earth-modeling) and dynamic modeling (predictive and prognostic/validation) helped to understand production behavior, quantify impact of uncertainty parameters on reservoir response and estimate oil recovery. Finally, poststeam cores were acquired in the SST and the LSP pilots, adjacent to existing presteam cored observation wells, and detailed analysis (routine and SCAL) helped to quantify the residual-oil-to-steam and steam-rock interactions.
The learnings from the phased piloting approach to this carbonate field are vital to mitigate key uncertainties for full field steamflood development (FFSFD). The lessons learned and the best practices for successful steamflooding of carbonate reservoirs will be highly leveraged for optimum development design.
Environmental and economic concerns have led to an increased interest in seismic stimulation as an alternative enhanced oil recovery (EOR) methodology. Seismic stimulation, achievable with the implementation of a single tool, requires significantly lower investments than gas, thermal, and chemical injection methods, while making minimal environmental impact. Applied Seismic Research (ASR), based in McKinney, Texas, has placed more than 200 of its proprietary seismic stimulation tools in more than 50 locations, including fields in Arkansas, California, Canada, Egypt, Kansas, Mexico, Oklahoma, Oman, and Texas. This article will examine the operation of the tool and highlight the EOR results achieved in a variety of formations. Seismic stimulation is the harnessing of low-frequency, high-energy elastic waves to mobilize oil.
The report card for unconventional oil and gas producers from a leading industry analyst is A+ for growth and F- for paying back investors. But Bob Bracket, senior analyst for Bernstein Research, who created the report card, said he is seeing signs of change. On the production side, the industry is struggling to keep up with the Permian Basin because output is exceeding available pipeline capacity. On the supply side, the industry may be moving away from pushing production so hard it drives down prices to levels where no one can make money. As this business has recovered from the last down cycle, it has “behaved for the last 6 quarters,” he said.
Figure 1—Well map showing location of selected pilot pattern and peripheral injection wells. A carbon-dioxide (CO2) -foam enhanced-oil-recovery (EOR) pilot research program has been initiated to advance the technology of CO2 foam for mobility control in a heterogeneous carbonate reservoir. A more-integrated multiscale methodology was required for project design to further understand the connection between laboratory- and field-scale displacement mechanisms. East Seminole Field The East Seminole Field in the Permian Basin of West Texas was discovered in the early 1940s with an estimated 38 million barrels of original oil in place (OOIP). The field was developed throughout the 1960s, producing 12% OOIP through pressure depletion.
In my previous features, I discussed the challenges facing carbon dioxide (CO2), both technical and economic. By far the biggest use of CO2 is in enhanced oil recovery (EOR). In this feature, the focus is on overcoming the biggest challenges facing CO2 EOR—gravity override and mobility. When CO2 is injected into a reservoir, it has a tendency to rise and segregate to the top of the reservoir, thereby bypassing some of the remaining oil. This is primarily because of the density difference between CO2 and reservoir fluids.
Foam-assisted CO2 enhanced oil recovery (EOR), commonly referred to as CO2-foam EOR, has been proposed as an effective technology for correcting sweep inefficiencies caused by gravity segregation and reservoir heterogeneity. The central concept of CO2-foam EOR is the in-situ generation of a viscous emulsion of CO2 and water stabilized by a surfactant at reservoir conditions.
Steamflooding technology introduction into hydrocarbon recovery operations often brings with it unwanted unavoidable mineral scaling challenges. In this example, steamflood generated calcium carbonate scale caused downhole equipment failure during cyclical steamflood stimulation (CSS) operations. The precipitated scale was effectively removed via mineral acid tubing wash, however mineral acid use for ad-hoc scale dissolving duty added significantly to the corrosion burden of well production tubing strings already regularly exposed to aggressive high concentration mineral acid during near wellbore matrix stimulation treatments. Scale inhibitor squeezing was proposed as a proactive alternative to mineral acid for downhole scale mitigation, and is the subject of this case history. The Middle Eastern heavy oil (HO) field has experience in employing scale inhibitors for topside scale control, but has limited experience in scale squeezing, and no experience of scale squeezing cyclical steam flooded wells. The initiative therefore presented some interesting challenges with respect to the Scale inhibitor selection (thermal stability concerns, compatibility and calcium carbonate efficacy concerns), where to place the scale squeeze in the CSS treatment programme, the squeeze design and its placement within the CSS well, and introduction and execution of routine well scaling health monitors for assessing the performance of the scale squeeze across the full CSS life-cycle.
Detailed bullheaded scale squeeze designs were prepared for two pilot HO field CSS wells that had experienced CaCO3 scaling. Once prepared, the squeeze treatments were quickly scheduled and executed without significant issue - either during treatment application or post-squeeze/steamflood return. The well brine monitors (brine ion composition, residual scale inhibitor and suspended solids) revealed interesting trends during the surveillance phase, but most importantly showed that the scale squeezes performed according to design and successfully maintained the wells free of CaCO3 scale, up to and including the 266 days post-steamflood, at which point routine well produced water sampling was discontinued. After 360 days (at the final review meeting) the field operators advised that both squeezed wells were still in operation and had experienced no scaling downtime.
Carbon-dioxide (CO2) injection is a successful enhanced-oil-recovery (EOR) technology that has been deployed extensively in the Permian Basin of West Texas, enabled by CO2 mostly produced and transported from naturally occurring CO2 reservoirs in Colorado and New Mexico. Further expansion of CO2 EOR has been limited by the availability of affordable CO2 rather than the existence of suitable target reservoirs for redevelopment with CO2 EOR. The US Department of Energy estimates that 67 billion STB of economically recoverable next-generation CO2-EOR oil exist in US conventional reservoirs, with significant potential identified in other oil provinces around the world. This situation may be about to change. On 9 February, Congress passed and the president signed into law a budget agreement that included language to expand a 2009 tax credit for CO2 capture and storage known as 45Q.
Brown, Joel (Chevron Corp) | Kumar, Raushan (Chevron Corp) | Barge, David Lee (Chevron Corp) | Lolley, Christopher (Chevron Corp) | Lwin, Al (Chevron Corp) | Al-Ghamdi, Saleh (Chevron Corp) | Bartlema, Ruurd (Chevron Corp) | Littlefield, Brian (Chevron Corp)
The 1st Eocene is a multibillion-barrel heavy-oil carbonate reservoir in Wafra field in the Partitioned Zone (PZ) between the Kingdom of Saudi Arabia and Kuwait. A large-scale steamflood pilot has been successfully completed in the 1st Eocene reservoir. The large-scale pilot (LSP) was the first multipattern steamflood in a carbonate reservoir in the Middle East, and consisted of sixteen 2.5-acre inverted 5-spot patterns with associated steamflood and production facilities. The primary objective of the LSP was to identify and mitigate technical and economic risks and uncertainties in carbonate steamflooding to assist in the broader Wafra full-field steamflood development (FFSFD) decisions. The key technical uncertainties related to the steamflooding in 1st Eocene reservoir were identified, categorized, and prioritized. These were then used as a basis to create surveillance and subsurface response plans. Success measures were developed to assess success in steamflooding this carbonate reservoir. These success measures were derived from the key metrics that were prerequisites for the FFSFD. The pilot met all the success measures, thereby mitigating the key technical uncertainties, and opened the path to FFSFD. This paper describes the elements of pilot planning and the results achieved during pilot execution. The emphasis, specifically, is on the achievements against the success measures set for the project; the insights into the pilot behavior from detailed analysis of production, pressure, and temperature data; and the progress made in identifying and mitigating key uncertainties in carbonate steamflooding.