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)