TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn Abu Dhabi offshore carbonates, it is recognized that fractures play an important role in influencing reservoir flow and connectivity both vertically (between reservoir units) and areally within the same reservoir unit. Image logs and borehole seismic surveys have been run to extensively identify fracture location and direction to understand the flow path of these reservoirs. However, in this paper an advanced step has been achieved in quantifying the fracture permeability from Conventional Logging Data, which is Micro-Resistivity Log, aided with Gamma-ray and Neutron-Density porosity logs. We all realized how vital, useful and critical this type of information would be as an input to reservoir simulators. This paper presents two techniques that have been developed to determine fracture permeability in reservoir rock and dense zones, these two techniques are merged to call it UFLIP (Universal Fracture Log Integrated Permeability).

Accurate water saturation estimation in thin carbonate reservoirs is one of the major formation evaluation challenges in horizontal wells. This is mainly due to the strong shoulder bed effect of thick dense sections on the resistivity logs recorded in thin porous reservoir layers, particularly in horizontal wells.The performed work implies correction of the high resistivity log data acquired while drilling horizontal well sections by means of resistivity modeling. This has been achieved by building a forward model for the resistivity data acquired in the deviated section of the overlying reservoirs in water injector wells, where the porous section is thick and the shoulder bed effect is minimal. The resistivity model construction is based on the relationship of the deep and shallow Laterolog resistivity to the neutron porosity log responses measured in the thick reservoir sections. The established model equations are used to construct deep and shallow resistivity logs in the horizontal sections of thin reservoirs by resistivity inversion using the neutron porosity log data.Several well data sets have been tested and the results were complimented by test data, formation tester fluid sample analysis, Dean Stark measurements and core data. The results obtained confirmed that the resistivity inversion technique is applicable to compute water saturation in both the flushed zone (Sxo) and the un-invaded zone (Sw) for horizontal well sections drilled across carbonate reservoirs. The application of the inversion process allows generating resistivity log responses corrected for the tight shoulder bed effects, and providing more accurate water saturation estimation.

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Quantifying gas saturation in carbonate formations through cased logging remains an elusive objective. Unsolved gas saturation quantification in cased hole was always thought to be due to unknown or uncontrolled borehole completion, casing, cement, acidizing, perforation, invasion and/or formation damage. Several techniques have been developed in the past to correct for the cased-hole thermal neutrons logs in an attempt to normalize the data through laboratory experiments, correction charts or open hole computer processing of effective porosity (PHIE). In Abu Dhabi offshore lower Cretaceous reservoirs, joint petrophysical & reservoir engineering efforts have shown that most of these automated corrections and/or normalizations are not capturing the real environmental changes from open-hole (OH) to cased-hole (CH). The reasons behind it are:Open-hole neutron logs were not considered as the reference; instead, old technique uses PHIE (Effective Porosity).Casing and cement corrections are based on a homogenous isotropic model.There was no proper resolution matching between OH and CH and edge effect corrections applied to pulse neutron data. Therefore, new technique is developed and presented in this paper; it is called "HYDGO" (Hydrocarbon Density Determination for Gas and Oil). This technique utilizes several back-to-back OH and CH log data information to carefully eliminate the CH environment effect. This is done by developing multi-variable-correction model that incorporates OH bulk density, water saturation, thermal neutron porosity and invasion. This procedure has led to the development of hydrocarbon density and gas saturation determination. Introduction Gas saturation is one of the vital requirements in reservoir management due to subsequent changes in reservoir fluid saturation and characterization after starting gas injection. In general, Gas injection is important for:Maintaining reservoir pressure.Enhancing recovery to reach as closest as possible to residual oil saturation.Changing oil properties with miscible gas injection to achieve better recovery Therefore to assure that gas injection project can achieve its maximum value, HYDGO technique has been developed to:Determine gas saturation (Sg).Utilize pulse neutron logs data for purpose, as it is the only possible formation evaluation logs can go through tubing. HYDGO technique was developed and tested in Gas Injection Pilot Project in one of major offshore field in Abu Dhabi. The G-I-P-P consists of four wells, two horizontal injector wells drilled into two different subzones, one zone is designated to be a secondary gas flooding zone and the other is tertiary gas flooding zone. Also one observer and one producer are also drilled 500 meter far away from injectors. Several logs were programmed and run in this project, for both OH and CH sections. Full suite of OH logs was run to establish a baseline saturation comparison to be used later with CH logs. The OH program consists of:Induction and Laterolog ResistivityThermal and Epithermal Neutron PorosityDensity with PE (Photo Electric factor)

In one of the biggest carbonate reservoir in offshore Abu Dhabi that has been producing oil for more than 40 years, oil potential evaluation is affected by many uncertainties as evaluated via pulsed neutron technology across perforated intervals.The Acid used to stimulate the wells after workovers affect the responses of the pulsed neutron logs. Efforts have been exerted to eliminate this effect. Observations from this field showed that the acid life cycle in the formation can be extracted by comparing and correlating several pulsed neutron sigma logs that are acquired over the years across the same perforated intervals.It has been noticeable that one of the most influential parameters in removing or eliminating acid existance in reservoir rock is water production, otherwise acid effect on pulse neutron sigma log interpretation remains, resulting in calculating high water saturation across dry oil producing zones.Understanding this acid effect life cycle helped understanding reservoir performance and reducing uncertainty of pulse neutron sigma interpretation. This paper is showing these observations in our field and is detailing acid effect modeling on pulsed neutron log responses.