The extreme heterogeneity of carbonate reservoirs in the form of fracture corridors and super-permeability thief zones present challenges to the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Foam-based conformance control is a relatively new technology especially its use for deep diversion in high-salinity and high-temperature conditions. In this work, a laboratory study was conducted to develop and evaluate a foam-based conformance control technology for application in a high-salinity and high-temperature carbonate. Foaming agents (surfactants) were first screened for their suitability with regard to reservoir temperature and salinity where properties such as foamability and foam stability were measured. The best performing surfactants were then used to study the foam-induced mobility reduction across a core composite. The experiments were conducted at reservoir conditions. Foam stability and decay were also investigated in those permeability reduction experiments. Brine and crude oil were injected after foam formation where observed pressure drops allowed quantification of foam stability and decay; hence, the sustainability of mobility reduction. Finally, the potential improvement in reservoir contact and hence oil recovery were examined by oil displacement experiments conducted in specially prepared heterogeneous composites. For the studied conditions of high salinity and high temperature, foaming agents of the amphoteric family as well as one manufacturer proprietary surfactants blend were found suitable in terms of salt tolerance and foam stability. Using the proprietary blend and without oil in core, the generated foam reduced fluids mobility by a factor of 12. The attained mobility reduction was lower in presence of oil but was still acceptable for flow diversion purposes. Using the proprietary blend and with oil in core, the generated foam reduced fluids mobility by a factor of 6 (compared to 12 without oil in core). Oil recovery improvement with foam placement was also found to be significant. These results demonstrate the potential of foams for carbonates with harsh salinity and temperature conditions.

Production logging at multiple rates is used to correlate passive inflow device (ICD) completion designs to actual downhole flow rates for performance validation and design improvement. Accurate steady-state multi-rate production logging is quantitative proof of design for completion evaluation. When low rates are recorded first in wells that have not been fully unloaded, and then are followed up with high rate passes, the PI per compartment values may change due to unloading. When this occurs, the simulations will not match both rate curves because the production profile has changed in the time it took to log the two rates. Unloading at high rates may result in rapid wellbore cleanup, and the production-profile changes that are due to the cleanup rates will be evident. When this occurs, the utility of the lower rate PLT dataset is greatly diminished. This paper discusses the importance of performing production logging tests for the evaluation of flow contribution in ICD completions. Sandstone and carbonate case studies are presented that will illustrate the benefits of using a properly sequenced logging strategy for ICD completion performance evaluation. Multi-rate and high-to-low rate-production testing is highlighted, since it has resulted in improved well clean up and productivity. Multi-rate production logging also helped to differentiate between non-productive and the damaged zone sections along the horizontal. This comparison verifies the value gained for operators when an appropriate production-logging test design is put into practice.

Thin reservoirs that are only a few feet in thickness present a clear challenge to development specially when coupled with fractures, lateral heterogeneities, and structural uncertainties. This paper discusses the challenges associated with the development of a thin zone located at the top of a carbonate reservoir as well as the strategies implemented to overcome these challenges and develop the zone successfully. Due to the lower rock quality when compared to the underlying zones and extreme thinning, this zone could not be produced through the conventional vertical wells historically. Through the strategic monitoring program implemented in the field, an opportunity to place direct production from this zone has been identified specially in the mature areas of the field where the lower zones are fully swept after decades of continuous production whereas a thin zone at the top of the reservoir is unswept. Capitalizing on this opportunity, a strategic development plan has been initiated. This plan calls for placing horizontal laterals in this zone utilizing recently developed fit-for-purpose well placement and completion technologies. To successfully develop this challenging zone, several strategies have been implemented. First of these was strategic well planning where a systematic methodology was implemented to evaluate and develop this zone. The most promising target areas were located through comprehensive evaluation of the area, with detailed geological modeling. Secondly, advanced geosteering with a rotary steerable system (RSS) has been utilized to efficiently place laterals in the upper lobe of the targeted zone. Advanced completions, using inflow control devices (ICDs), were utilized as a fit-for-purpose to mitigate the counter effect of fractures and/or pressure differences across the horizontal section. The development program has been very successful in yielding significant production gains.

This paper presents the re-development strategy employed to recover attic oil from the highly-fractured crestal area of a carbonate reservoir. Optimum re-development strategies for the crestal area, along with planning and execution incorporating Best in Class (BiC) reservoir management practices are discussed.The crestal area was previously developed using full penetration vertical wells. After many years of continuous production and nearby injection, oil production rates in these crestal wells have declined with increasing water cut.The re-development strategy has been tailored to exploit this challenging opportunity and to maximize the production efficiently with selective placement of horizontal skimmer wells at the very top of the structure. Fit-for-purpose completion technologies were deployed to address the effects of the extensive fractures. Tapping oil continuously flowing into the crestal area by displacement, gravity, and capillary mechanisms, this re-development strategy has resulted in efficient and sustainable production.

Reservoir monitoring is an important aspect of prudent reservoir management to sustain productivity and achieve higher hydrocarbon recoveries. Monitoring is a process that comes in various forms, such as that of flood front advancement and reservoir saturation changes and quantification. Designing and implementing an effective monitoring program to track fluid advancement and quantify remaining oil saturation is a reservoir management best practice that ensures optimum sweep is achieved; and so is crucial for all fields, regardless of their state of maturity. The necessity for such programs becomes more critical as fields mature. Reservoir saturation monitoring programs are usually faced with several challenges, including: mixed and low fluid salinity, tool limitations, borehole conditions and reservoir heterogeneity. Overcoming these challenges requires comprehensive programs that encompass adoption and integration of various derived saturation techniques. This paper will discuss a reservoir monitoring program of a large carbonate field that has produced continuously for several decades. The monitoring program includes "key monitoring wells" in addition to drilling new evaluation wells that are strategically selected and are mostly located in well flooded areas. Time-lapse production and fit for purpose saturation logs are run in the existing wells, while extensive in situ measurements of fluid saturation are collected in the case of the new wells, to monitor saturation changes and track the movement of fluids. The paper will also discuss the various methodologies adopted to address the aforementioned challenges. It will illustrate how the monitoring program has aided in tracking fluid movement, quantitatively determining fluid saturations and assessing sweep efficiency (Ed, Ev and Ea). In addition, the paper will show how the collected information was a catalyst in identifying sweet spots in flooded regions, and therefore guiding development activities for maximizing hydrocarbon recovery, especially from mature areas.