For pressure maintenance purpose peripheral wells have been used to inject sea water into a carbonate reservoir offshore Abu Dhabi. The injected water preferentially follows the path of the of higher permeability zones, since injection is done into formation water below oil water contact. Though the sea water front movement in the reservoir has been estimated indirectly via numerical reservoir simulator, successes of direct methods have been limited by the injection volume and environmental effects.Direct spatial measurement of the injected sea water front within the reservoir is important to evaluate the efficiency of pressure maintenance by peripheral water injection, also considered an important step in tuning simulator parameters, and optimizing the Field Development Plan (FDP).Although there is strong water salinity contrast between the injected and original reservoir water in this field, resistivity-based methods can be affected by variations in the reservoir rock cementation factor, while cased hole logs can be affected by environmental effects such as hydrochloric acid effect commonly seen in carbonate reservoirs after stimulation.This technique that utilizes open hole Pulsed Neutron Sigma measurement of Logging While Drilling (LWD) enables petrophysicists to distinguish and determine injected water separately from formation water, independent of Archie-based resistivity method. Also this technique provides a new methodology to calculate cementation factor (m). Successful application of this technique in an offshore Abu Dhabi carbonate reservoir is presented here.

Sand production can be challenging for many operators in unconsolidated formations. The production of formation sand and fines can cause erosion damage to both surface and downhole equipment, resulting in major well intervention and sand disposal costs. Conventional resin consolidation systems have been successfully used to prevent solids production in short, homogenous intervals. However, resin consolidation attempts in longer intervals have resulted in erratic success rates, which could be attributed to a lack of complete and uniform treatment of the entire interval length. A recently developed aqueous-based resin (ABR) system has helped provide effective and efficient treatment of significantly longer intervals, has improved health, safety, security, environmental (HSSE) compatibility, and can help improve various operational considerations. This paper discusses results of laboratory testing and the subsequent successful treatment using the ABR system within a well located in Nile Delta, which was the first attempt of its kind in Egypt. Sieve analysis revealed unsorted formation sand, which usually requires a gravel pack completion, rather than a standalone screen; however, because of limitations with respect to wellbore diameter (5 in.), it was difficult to complete the well using conventional gravel pack completion methods. Additionally, the well had a history of unsuccessful treatment using a non-resin product, which modifies the surface potential charges of the sand grains and reduces the repelling forces between them. The well was still producing sand after that treatment; thus, the decision was made to treat the interval using the ABR system. Thereafter, hydrocarbon production, at a rate of 5.5 MMscf/D, was monitored and sand production from the well decreased by more than 95%, with no impairment to hydrocarbon production.

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.

Pulsed neutron logging is currently the most commonly used technology for cased hole formation saturation analysis, providing data for reservoir monitoring and management. The common pulsed neutron log measurement is the formation capture cross section (Sigma). The data can be logged at a relatively fast logging speed. Water saturation analysis using the Sigma log requires high porosity and known formation water salinity. Errors in the Sigma log interpretation can result from the uncertainties of water salinity values, which usually change, for example, due to mixing of the hypersaline formation brine with the low-salinity injected seawater. Heterogeneity and changes in the carbonate petrophysical properties also play a role in magnifying the magnitude of water salinity changes. Carbon/ oxygen ratio logging (C/O) is salinity-independent and can be applied to overcome the problem, but the physics of the measurement usually require multiple passes with lower logging speeds than Sigma logging. This paper introduces a novel pulsed neutron logging methodology to help overcome the mixed-water salinity problem and produce a reliable water saturation interpretation for updating fluid front maps. First, the pulsed neutron tool was operated in Sigma mode to cover the full target reservoir interval in a single pass. The tool was then switched to the C/O mode with multiple passes for 50ft only at the top of the target reservoir. Monte Carlo modelling was applied to the C/O data to calculate the water saturation. The C/O result was then used with the Sigma log data to inversely calculate the Sigma water using a Sigma-based material balance equation across the same interval. The final water saturation across the full interval was estimated by using the calculated water salinity and the Sigma data. Through the application of the proposed methodology, we successfully measure the target formation saturation information in an acceptable operating time, when compared to conducting the conventional C/O logging across the full interval. The results show that the estimated formation water salinity is close to that value of drilling mud filtrate; the water saturation is slightly lower than that from the openhole resistivity interpretation. This paper introduces how to optimize a pulsed neutron logging program that combines the C/O and Sigma measurements to enhance the offshore operations efficiency, minimize the water saturation interpretation uncertainties, and support future field development planning.