Second EAGE Workshop on Well Injectivity and Productivity in Carbonates

Over the past decade, significant advancements have been made in the prediction of the petrophysical properties of reservoir rocks using x-ray micro CT based digital rock physics (DRP) workflows. Such techniques now enable static and dynamic petrophysical properties, such as bulk and effective porosity, single phase permeability, capillary pressure and relative permeability to be derived directly from pore-scale images of rocks. The derivation of a comprehensive suite of petrophysical properties previously required time consuming laboratory analyses using standard core plugs, typically derived from cores, negating the use of smaller rock fragments (i.e. drill cuttings) which typically provide more representative coverage of penetrated units along the length of the well bore.

In this study, the impact of subvolume dimension upon image based predictions of porosity and permeability have been investigated, in order to provide improved insights into subvolume selection in carbonate rocks. Two lithologies (Estaillades and Ketton Limestone) displaying different degrees of pore-scale heterogeneity were studied. A pore network extraction routine and a single phase simulation code have been used to estimate permeability, with voxel counts used to establish porosity. Calculations are repeated within progressively dilated kernels, enabling the statistical homogenization of petrophysical properties with increasing subvolume size to be assessed.

In cased hole carbonate wells, perforations are utilized to connect the wellbore to the formation, providing a conduit for stimulation fluid injection and reservoir production. Conventional hypotheses predict that when acid is injected in perforated carbonates, wormholes should nucleate at the tip of the perforation tunnel ( Huang et al. 2000 ). This assertion is based on models for the leak-off distribution along uniform-diameter perforation tunnels in which the effects of crushed zone damage are ignored. In contradiction to this hypothesis, recent studies have shown many examples in which dominant wormholes nucleate well behind the tunnel tip in perforated core experiments ( Rabie et al. 2013 ). This is interesting considering the fact that the effects of flow localization at the tunnel tip are believed to be exaggerated in axial core flow experiments owing to the influence of the no-flow boundary.

This study focuses on Mishrif formation in Rumaila oilfield. the dynamic behaviour of thief zone and its impact towards production and injection are presented. Results indicate that thief zones are observed in this carbonate formation. Surveillance data (PLT) indicates that there are very productive thin layer, which contribute more than 75% production with the thickness of less than 10% of the total net pay thickness. In addition, and the distribution of thief zone are characterized based on PLT, which indicates that thief zone development has intimate relationship with facies and diagenesis.

This paper presents a realistic synthetic case study based on data and materials integrated from public domain research carried out by the authors. The selected geological formation contains an abundance of oil reserves in the Middle East, and is classified among the most economically important. In comparison with on-site well testing operations, the computer-based workflow used in this study does not require to shut in any well or change production. Hence, the oil field production and water injection can be maintained suitably and sustainably. It is proposed to build multi-layered sector models to better capture both overall regional reservoir behavior and local effects between alternating rings of production and injection wells, even between individual multi-lateral wells and in the wellbore vicinity. It is shown that different horizontal variogram range influences phase productivity indices of wells, which may highly impact the accuracy and precision of production forecasts in planning field development, designing well stimulation operations and enhanced recovery processes.

The presented case study does not intend to replace any real full field reservoir model, but this can serve for quick feasibility and evaluation studies allowing to improve the workflows used by oil and gas companies faced similar challenges.

This paper discusses the possible application of Fiberglass casings and tubings for the use in the Injection wells. This paper initially outlines a basic review of fiberglass piping in the industry and the manufacturing process. Field issues identified through literature, interviews and operator experiences have been presented and analyzed. Methods and avenues to address these issues have been researched, and a look to the future of fiberglass in the field is provided. Pipe failure, fire safety, injection and handling have been addressed.

The resistance of Fiberglass tubulars to corrosion is well documented, and potentially can provide benefit and advantage where conventional carbon steel tubulars face extensive corrosion issues, such as in corrosive injection environments. Very little research on this specific issue has been published. This paper aims to shed some light on not only the benefits of fiberglass as a corrosion-resistant material, but document field-based experiences on use of fiberglass in the field. This paper proposes that fiberglass casings and tubings are very suitable for injection wells and it aims to pave the way to further adoption and research of fiberglass in applications such as for corrosive injection environments.

Acid injection into carbonate reservoirs aims to improve the injectivity and productivity of wells ( Schechter 1992 ). Indeed, under the acid effect, the carbonate rocks can be dissolved, which increase the porosity and permeability around the wells. Various approaches have been used to model chemical reactions during acidification processes and this considering different scales (pore to reservoir) and different flow regimes ( Golfier et al. 2001 ; Cohen et al. 2008 ; Portier and Vuataz 2010 ; Maheshwari and Balakotaiah 2013 ; Maheshwari et al. 2016 ).