Compatibility Coreflood Studies Explore Formation Damage in Tight Reservoirs
Authors: Carpenter Chris 
Published: April 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 207764, “Case Study of Identifying and Minimizing Formation Damage in Tight Reservoirs Caused by Drilling Fluids in Abu Dhabi Onshore Operation Using Compatibility Coreflood Studies,” by Raymond Saragi, Mohammad Husien, and Dalia S. Abdullah, ADNOC, et al. The paper has not been peer reviewed.

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The authors examine formation-damage mechanisms caused by drilling fluids in tight reservoirs in several onshore Abu Dhabi oil fields. Three phases of compatibility corefloods were performed to identify the potential of improving hydrocarbon recovery and examine reformulated or alternate drilling muds and treatment fluids. The compatibility corefloods on tight reservoir cores, along with high-resolution quantifications and visualizations, identified damaging mechanisms and helped identify potential to improve hydrocarbon recovery and treatment-fluid options.

Introduction
The operator examined drilling-mud performance for UAE fields including Bab, Rumaitha, Qusahwira, Sahil, and Mender. Results appeared to be good in high-permeability zones but not in lower-permeability zones. A multiphase compatibility study consisting of a series of coreflood simulations analyzed both producer and injector wells, but the complete paper focuses on the producer wells. The use of nano-computed tomography (CT) scans and cryogenic scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) as interpretative tools provided insights into the coreflood results (55 of which are presented in the complete paper).
The reservoirs consist of Lower Cretaceous carbonate sediments. This study examined lower-permeability zones; the results shown in the complete paper are only from the tight samples below 15 md. The samples used in the study are detailed in Table 1 of the complete paper and represented the following reservoirs:
- Bab (wells coded BB-1, BB-2, BB-3, BB-4, BB-5, BB-6, and BB-7; 0.1–15-md gas permeability)
- Mender (well coded MN-1; 3–12-md gas permeability)
- Qusahwira (wells coded QW-1 and QW-2; 0.5–1-md gas permeability)
- Rumaitha (well coded RA-1; 2–15-md gas permeability)
- Sahil (well coded SA-1; 2–4-md gas permeability)

Methodology
Coreflood simulations were performed using specialized equipment capable of executing the study at reservoir conditions while eliminating artifacts such as corrosion. Accurate replication of reservoir conditions is important, especially where potential scaling exists.
Phase 1 examined permeability alterations and damaging mechanisms after application of the currently used drilling mud. The methodology is detailed in the complete paper, but the authors emphasize the use of interpretive tools in this process.
Phase 2 examined a series of reformulated and alternate drilling muds. Following the results of Phase 1, the current field mud was reformulated and examined as Reformulated Mud Formulation 1 alongside three alternate drilling muds from separate vendors.
Phase 3 built on Phases 1 and 2 by examining the incorporation of a displacement or treatment fluid as part of the operational sequence. The methodology for Phase 3 was similar to that used in the previous phases, with the addition of treatment-fluid application before drawdown.