Primary and secondary recovery processes produce about one third of oil in place, leaving significant volumes behind. For low permeability and highly saline carbonate reservoirs, exploiting these resources is often challenging and unfeasible either technically and/or commercially. In this paper we discuss the application of an emerging EOR technique that has shown promising results in the lab. Di-Methyl Ether (DME) enhanced waterflood (DEW) is a process in which DME is added to injection water, which upon injection into the reservoir, it preferentially partitions into the remaining oil. As a result, it swells the oil and reduces its viscosity which significantly improves oil mobility in the reservoir. Several core-flood experiments conducted in tight carbonate plugs have shown incremental recoveries of up-to 20% post waterflood. Additionally, the process provides significant acceleration to oil production, which would otherwise take several pore volume of water injection. After successful PVT and core flood experiments, a field trial has been designed to de-risk this technology which if successful would add significant reserves. The pilot will be implemented in a tight carbonate reservoir that has been under waterflood. Some key uncertainties this pilot will address include solvent utilisation, oil incremental recovery, solvent back production and impact of geology on the process. This paper discusses the key physical mechanisms of the process, pilot design and challenges of full field considerations. In addition, it also highlights key considerations when designing solvent-based EOR applications. The paper also highlights the need of lab work to mitigate operational issues prior to implementation. Calibrated numerical models were used to generate full field profiles, which show the need for a well optimised pattern design to make such processes feasible
Petroleum Development Oman's (PDO) portfolio of heavy-oil, fractured carbonate prospects and fields contains a potentially large number of EOR opportunities, many of which present unique subsurface challenges. In the context of evaluating one such field, an EOR screening approach was developed combining subsurface definition through a tailor-made appraisal campaign, coupled with technical & economic feasibility evaluation of candidate EOR methods and benchmarking against other fields globally. This paper presents the screening workflow that will serve as template for the evaluation of future EOR opportunities in heavy-oil, fractured carbonate discoveries in PDO.At the outset of the reservoir characterization of this field it was recognized that the application of any EOR technique would be challenging. High oil viscosities coupled with shallow depths render it a candidate for thermal EOR and potentially chemical concepts. However, key uncertainties in basic subsurface parameters such as reservoir architecture, matrix permeability, fracture spacing and (low) oil saturations, necessitated further data gathering before feasibility of any recovery mechanism could be concluded.Based on literature surveys and examination of showstopper properties, a first-pass screening of a multitude of thermal and chemical EOR methods was conducted. A probabilistic assessment of key subsurface parameters was conducted against which the candidate EOR techniques were ranked. This resulted in the identification of SAGOGD, CSS, ISC and novel-chemical flooding as the most promising EOR methods.For each of these methods the critical subsurface parameters and their impact were further assessed through the combination of (1) an appraisal campaign that included drilling of new wells, conventional production & pressure interference testing to constrain the uncertainties in these parameters and (2) Fit-for-purpose modeling (analytical analysis, sector modeling and full-field simulation) to check project feasibility.It was found that none of the thermal recovery methods are technically or economically feasible, but chemical methods are being investigated further. 2 SPE 155546
There have been a number of major heavy oil discoveries in Oman in recent years. In order to devise efficient and cost effective recovery mechanism careful and detailed subsurface understanding of these fields is critical. To this end, petrophysical understanding plays a critical role, as it represents a basic building block of the static and dynamic models. The field under study is a fractured carbonate reservoir with high viscous oil. It is believed that this reservoir has gone through various cycles of drainage and imbibition. Thus, in addition to the complex geology, understanding of fluid distribution and fluid mobility are among major challenges that detailed petrophysical evaluation needs to address. Understanding these parameters will help determine the feasibility of the recovery methodology to be adopted. This paper details a novel petrophysical workflow that integrates 3D NMR, multi array/multi frequency dielectric measurements, borehole images, and core analysis. The core analysis focused on capillary pressures, Dean-Stark, and rock typing. Fracture studies included detailed image analysis and extensive fall off test for understanding the nature and distribution of the fracture network in the reservoir. The wealth of well data coupled with geological and dynamic data reduced the overall reservoir properties and fluid distribution uncertainties.Dielectric data provided resistivity independent saturations validated by Dean-Stark data. Combining dielectric and 3D NMR data allowed better formation characterization and fluid type evaluation and their present day distribution. Additionally, this combination indicated that water is not at an irreducible state in the reservoir. This was supported by the core saturation height function which indicated that present day saturation should be much higher if the reservoir was in drainage mode. These results were crucial to evaluate development options, underlying uncertainty/risks of this reservoir, and design optimum future data acquisition requirements. TX 75083-3836, U.S.A., fax +1-972-952-9435
The field under study is a fractured carbonate of low matrix permeability (~15mD) and modest fracture permeability (<1200mD). The structure is relatively flat with a maximum movable oil column of 60m and a median thickness of 30m and is underlain by a strong aquifer. The live oil viscosity is 7cp. To date the field has recovered a small fraction of its STOIIP, mostly under natural depletion and WOGD. The field is scheduled for re-development by Cold Gas-Oil Gravity Drainage (CGOGD). The feasibility of a later phase of development by Steam-Assisted GOGD (SAGOGD) was evaluated and is the subject of this paper.The field's reservoir properties present a unique set of challenges for an SAGOGD development. Firstly, the relatively low oil viscosity at initial conditions is unfavourable for a large viscosity reduction by heating. Also, the extent of the structure together with the modest fracture permeabilities complicates the spread-out of steam over the field. Finally, heat transfer efficiency to the matrix is problematic given the small thickness of the reservoir and the large matrix blocks.The SAGOGD development strategy calls for simultaneous gas and steam injection by injectors that are spread out over the field, which stabilises the oil rim, spreads out the steam and reduces aquifer water influx. The incremental recovery over CGOGD was demonstrated to be substantial (16% of STOIIP) with an acceptable oil-steam ratio. Analysis of physical processes contributing towards recovery showed that viscosity reduction was still the main contributor to oil recovery.Significant uncertainties remain to be reduced before committing to an SAGOGD development. Besides the wide range of uncertainty in incremental recovery (+/-60% from the base case), water supply and disposal requirements are major challenges for the steam project. Whilst these latter are being evaluated, the initial phase of CGOGD will narrow subsurface uncertainties for SAGOGD development substantially. In this paper the subsurface elements of the study will be discussed.
1999. Naema's main interest lies in the area of interpretation and processing geophysics.
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