The Middle Minagish Oolite Formation is 450 to 550 feet thick interval of porous limestone reservoir, composed of peloidal/skeletal grainstones with lesser amount of packstone, oolitic grainstone, wackstone and mudstone in Umm Gudair field, West Kuwait. It is characterized by small scale reservoir heterogeneity, primarily related to the depositional as well as diagenetic features. Capturing reservoir properties in micro scale and its spatial variation needs special attention in this reservoir due to its inherent anisotropy. Reservoir properties will depend on the level that we are analyzing on reservoir (millimeter to meter scale). Here we used Electrical Borehole Image (EBI) and Nuclear Magnetic Resonance (NMR) to capture small scale feature of Umm Gudair carbonate reservoir and compared them with core data In present work, reservoir properties (including texture, facies, porosity and permeability) interpreted by the EBI shows good match with NMR driven properties and core data. Textural changes in image logs also match well with pore size distribution from NMR logs. Further highly porous zones which are considered either due to primary porosity or vugs match with larger pores of NMR logs and these corroborates with also core derived porosity. A good match has been observed between EBI, NMR and cored derived porosity. Permeability calculations have also been made and compared with core data. A detail workflow has been developed here to interpret reservoir properties on un-cored wells, where only low vertical resolution data is available. This technique is quite useful to identify the characters and mode of origin highly porous zones in reservoir section which are generally not identifiable by low resolution standard logs. This workflow will allow us to interpret the heterogeneity at high resolution level in un-cored wells, as results are validated with integration of EBI, NMR and core data.
Through decades of production and water injection, Umm Gudair reservoir fluid distribution have changed significantly, resulting in an increase of uncertainties on fluid levels and subsequent water cuts in production. Different well architectures have been implemented pilot holes, deviated wells or horizontals, but the development of such mature fields comes with inherent difficulties, as offset data does not necessarily reveal the current reservoir properties and fluid contact position. Frequently, costly and time-consuming additional operations such as cement plugs or sidetracks are required to resolve an unforeseen water saturation of the reservoir. However, these methods have a limited efficiency in reducing the water percentage over the time of well production. In this challenging environment, the Umm Gudair asset has implemented a different approach to well construction built upon the combination of an ultra deep resistivity tool with a previously unattempted benchmarking scenario for a look around inversion. Drilling a trajectory of 45° inclination in order to proactively identify the oil water contact (OWC) in the far field below, and confirm this forecast with an actual resistivity measurement during its penetration. This unprecedented process shows great opportunities in optimizing future well placement and production performances. The main inputs in this success come directly from the capability of the inversion of the electromagnetic measurements in various drilling conditions, as well as a thorough preparation and collaboration between the operator and the service company. Before implementing this technology, it is critical to assess the expected performance by understanding the different parameters which affect the performance of the tool. The study of the different offsets gave an overview of potential resistivity contrast between fluids and their contact positions. The pre-well study is therefore essential to optimize depth of detection (DOD) versus sensitivity through forward modeling of various frequencies and spacing selections. This phase is also necessary for the team to understand what can be expected from the service with the elaboration of different scenarios based on theoretical tool responses and communication protocol. This case study shows how an innovative scenario and collaboration between operator and service company reveals a new capability to place a well drilled at mid-angle in the lowest water saturated part of the reservoir using inverted resistivity measurements. The economic benefit and post job analysis conducted post well confirm the promising outlooks of utilizing an ultra-deep resistivity service in a mature field environment.
Minagish Oolite reservoir is a prolific limestone reservoir in Umm Gudair field underlain by an active aquifer situated in West Kuwait. The field has been on production for over 50 years and has been experiencing rising water production levels in the recent years. Understanding the movement of water in the reservoir is vital for maximizing oil recovery. During the producing life of the reservoir, the vertical movement of water is influenced by presence of flow barriers / baffles in the reservoir and how they are distributed in the vertical as well as areal direction. Understanding the lateral distribution of the flow barriers to fluid movement in the vertical direction has been a challenge throughout the production history of the field. Efforts have been ongoing in the past, to understand the movement of aquifer water in the vertical direction based on analysis of openhole log data, structural configuration, stratigraphy, well performance, production logging (PLT) results etc. These have resulted in developing a respectable level of understanding of the distribution and strength of barriers/baffles and their effectiveness in the field performance. In a recent campaign to reduce the rapidly increasing volume of water produced from Minagish Oolite reservoir, a large number of workovers were carried out based on the current understanding of the vertical barriers / baffles, resulting in bringing down the water-cut level appreciably. The paper analyzes the results obtained from carrying out the numerous workovers for water shut-off in the recent campaign. This analysis has been utilized in an attempt to improve the history match in the dynamic reservoir simulation, especially the water-cut history match. Whereas good match of long water-cut history before the recent water shut-off jobs indicates absence of serious issue of well integrity, transmissibility modifiers in the simulation model were required, in order to improve water-cut history match in the post water shut-off period. Thus, there is vast improvement in the simulation team's understanding of the lateral distribution and strength of barriers / baffles. This has greatly aided in the formulation of more pragmatic plans for future workovers involving water shut-off by squeezing-off or isolating watered out layers. The result is a more robust prediction of production profile from the future field development activities. The paper presents how the integrated approach of the open-hole, cased hole logs data with field performance in the history match process of simulation helps in the improvement of reservoir simulation modeling.
This paper presents results from integration of Production Logging Tool (PLT) data with image facies interpretation from high-resolution electrical images in a horizontal producer well in Kuwait. The Minagish Oolite Formation is a carbonate reservoir in the Umm-Gudair field which is characterised by packstone to grainstone with oolitic rich facies. Integration of fluid contribution along the producer hole from PLT measurement with image facies from electrical image logs will support completion strategy optimization. A PLT was deployed in horizontal producer well of 6.125 inch (bit size) with coil tubing, when both flowing as well as shut-in conditions with choke size (128+128)/64″. Liquid rate from PLT 2981 Barel fluid per day (BPD) was in agreement with surface Portable Gas Oil Ratio (PGOR) test rate (2975 BPD). During drilling, high-resolution of electrical image was acquired. The electrical image has range of conductive (darker) and resistive (brighter) features, where conductive image shows porosity such as vugs and resistive image shows less pore space such as cemented patches in carbonates. Based on PLT measurement, entire producer section was divided into six intervals, as below Interval A has 800 feet and interval E has 150 feet with production rate 56 BPD.Interval B has 300 feet which contributes 80 BPD.Interval C contributes 100 BPD and has 75 feet lateral section.Interval D has 300 feet lateral and contributes 92 BPD.Interval F contributes maximum liquid of 2590 BPD from 1350 feet interval. On integrating PLT and facies analysis result, it was found interval F which gave highest liquid rate of 2590 BPD has higher statistics of conductive features. Second highest production rate coming from interval C is also showing high amount of conductive image. Low production rate interval E shows lower statistics of conductive features. Image analysis shows interval C and interval F having resistive patches, dominant moldic porosity and nodular limestone. Low production rate intervals are characterized by facies of clean massive limestone with less secondary porosity. Facies analysis was exercised using electrical image log to characterize the reservoir. Identified image facies were mottled, bioclastic, vuggy, nodular, and clean to argillaceous limestone. Facies analysis based on conductive and resistive features from high-resolution electrical image has relationship with production rate from PLT. The study concludes that electrical image can be used to optimize completion design and hence to optimize production rate.
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