The Raageshwari Deep Gas Field, situated at the northern end of the Central Basin High within the onshore RJ-ON-90/1 Contract Area, Rajasthan State, India, was discovered in 2003. It is a tight lean gas condensate volcanics reservoir, with excellent gas quality of 80% methane and low CO2 and no H2S content. Since discovery, several appraisal wells have been drilled in the field and tested extensively. The wells have produced gas rates in the range of 2-4 MMscf/d with condensate gas production ratios in the range of 40-50 STB/MMscf. The drawdowns during the production tests have been high, in the range of 3000-4000 psi, indicating the very low permeabilities of the reservoir. This paper describes the tight volcanic reservoir, the reservoir fluid present in it and the well test analysis results from several wells drilled in the field. The reservoir being very tight, the well tests have been carried out for long time periods, extending beyond a month, to enable deriving of meaningful information. As during testing the pressure drops below the dew point in areas around the wellbore, condensate dropout is expected to occur, influencing the relative permeabilities for gas and condensate flow. Radial composite models have been found to allow reasonable matching of observed test behaviour.Several hydrofracturing jobs have been carried out in these wells. Well tests carried out after completion of hydro-frac jobs have also been analysed and presented.
The key objective of the CO2 WAG Pilots is to confirm improved sweep and to enhance oil recovery under CO2 WAG relative to water flooding. Two CO2 WAG Pilots are in progress in a giant Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with two vertical pilot observers. A detailed monitoring plan was designed and implemented to monitor pilots’ performance and track CO2 breakthrough and flow path. Injectivity of both water and CO2 was determined in the WAG cycles to investigate any loss of injectivity. The producers are being tested daily for oil rate, water cut, GOR using multi-phase flow parameters (MPFM) while portable test separators are used every quarter to validate these measurements. PVT analysis of produced fluids are being carried out on samples from portable test separators and MPFM sampling point to monitor CO2 content. Different gas and water tracers have been injected to trace the movement and breakthrough of injected fluids into the pilot producers. Carbon and oxygen-isotope analysis for produced and injected CO2 gas is also carried out to monitor CO2 breakthrough. RST logs in the observers demonstrate good sweep across different layers of the reservoir and show that WAG is providing mobility control to CO2. Several data sources were analyzed to determine CO2 breakthrough time and the CO2 flow path. Analysis of CO2 in produced gas has determined the timing of CO2 breakthrough. This is supported by the isotopic analysis of injected and produced CO2 in pilot producers and near-by producers. The tracer analysis results unambiguously identify the source of the produced CO2. Injectivity analysis of both CO2 and water showed injectivity of CO2 was either the same or higher than water injectivity. Moreover, no loss of injectivity was observed between WAG cycles. The pilot has been operated successfully without HSE issues since 2016. Corrosion logs are acquired within the extensive monitoring program along with inhibitor injection to avoid any Asphalting deposition. The paper discusses the performance of the first multi-well CO2-WAG pilots in a giant onshore reservoir in Abu Dhabi which is used to de-risk multiple CO2 WAG full field projects in ADNOC reservoirs. It also highlights the importance of the different reservoir monitoring tools for improved understanding of the pilots which will be used as a basis for implementing CO2 WAG for the full area development.
The Mangala Field is located in the northern Barmer Basin of Rajasthan state, India. The basin is a Tertiary rift, predominantly consisting of Palaeocene-Eocene sediments. The Mangala Field was discovered in January 2004 and brought on production with hot water flooding in August 2009. The main reservoir units in the Mangala Field are the fluvial sandstones of the Fatehgarh Formation. The Fatehgarh Formation in the Mangala Field is subdivided into 5 reservoir layers termed FM1 (top) to FM5 (base). The lower part of the Fatehgarh Formation (FM3 to FM5) are dominated by well-connected sheet flood and braided channel sands, whilst the Upper Fatehgarh Formation (FM1 and FM2) is dominated by more sinuous, laterally migrating fluvial channel sands. The FM-1 unit hosts approximately half of the oil in place. A detailed fine layer geological model was built for the Mangala Field incorporating all relevant data from the field generated over the last couple of years. A set of 100 realizations of the geological model were generated. All of the realizations for FM-1 layer were simulated in a commercial streamline simulator using the available historical production data for FM-1 wells. The paper discusses the results from these multiple realization runs and the inputs given to the geological model which was used to improve the model further. These runs helped in identifying the areas where sand connectivity was low due to presence of some baffles or channel boundaries and needed improvement, to match fluid flow in the reservoir. After incorporating the PLT data into the dynamic model, the well wise water cut resembled the actual w/c and improved the confidence level on the geological model. The paper also discusses well allocation factor estimates for each producer and injector pair from the streamline simulation model for different injection patterns in FM-1. The well allocation factors helped in understanding the level of support each producer is getting from the nearby injectors
Assessing CO2 EOR in different areas of a field with different rock and fluid properties requires proper dynamic reservoir modelling. Good SCAL data is a key input to the dynamic model. Consequently a comprehensive SCAL program was designed for a super giant carbonate reservoir, onshore Abu Dhabi, for modeling CO2 EOR process in secondary & tertiary conditions. A careful selection of the core material based on a Petrophysical Group (PG) review was performed to make the experiments representative of key areas of the field in which CO2 flood is planned or studied.Laboratory experiments were designed at full reservoir conditions with H2S oil bearing, and to assess possible impact of H2S on displacement efficiency. Water-oil relative permeability tests showed insignificant impact of H2S, compared with non-H2S tests on cores of different PG's. Injectivity issues and importance of brine composition on water mobility were identified. Trapped gas to water and oil were also mapped successfully.The comparative analysis of CO2 EOR flooding scenarios using long composite cores with continuous CO2 injection and CO2 WAG were also performed. They indicate higher displacement efficiency with continuous CO2 injection. Tests were also conducted on composites with non-H2S live crude, representative of reservoir zones with little or insignificant presence of H2S.This study indicated for the first time in the published literature, the impact of H2S in water-oil relative permeabilities of carbonates at full reservoir conditions. The gas process displacement efficiency tests also verified negligible impact of H2S (up to 12%) in CO2 EOR 1D core floods.
Two CO2 WAG Pilots are in progress in an Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with 2 vertical pilot observers to monitor the movement of flood front away from the injectors. The pilots are being monitored based on a detailed reservoir-monitoring plan. The paper discusses in detail various activities and the results related to the pilot monitoring. Methods, Procedures, Process The wells are being tested for oil rate, water cut, GOR on a daily basis using MPFM. For calibration purposes portable test separators are used every quarter to validate the rate, water cut and GOR measurements. Separator PVT samples from pilot wells are collected every quarter for PVT analysis. In addition PVT samples are also collected from the pilot wells and nearby wells every month from the sampling point near MPFM to monitor the CO2 content in the produced gas. Online CO2 analyzer is fitted on the surface flow line connecting pilot wells to the RDS to provide continuous measurement of CO2 in the produced fluid. Produced water is also sampled for detailed compositional analysis. Different gas and water tracers have been injected through the pilot injectors to trace the movement and breakthrough of injected fluids into the pilot producers. Sampling and analysis for tracer is carried out on a regular basis. Carbon and oxygen Isotope analysis for produced and injected CO2 gas is also carried out in order to monitor the breakthrough of injected CO2 into the pilot producers. There is a good difference in the carbon and oxygen isotopes of injected CO2 and the CO2 present in the reservoir. To monitor the changes in water and gas saturation with time across different layers a set of Pulsed neutron (RAS) logs are run in the observers on regular basis. PLT logs are run in the injectors and producers to check the distribution and conformance of the produced and injected fluids along the horizontal wellbore. Walk away VSP surveys are being carried out on regular intervals for one pilot to monitor the injected fluids distribution in the pilot area. The paper describes all these reservoir monitoring activities in detail. Results, Observations, Conclusions Analysis of Carbon oxygen RST logs are helpful for tracking fluid saturation changes and CO2 movement across the logged intervals. The RST logs in the observers demonstrate good sweep across different layers of the reservoir. Analysis of CO2 in produced gas has resulted into correctly pointing out the timing of CO2 breakthrough in the producers. It is well supported by the CO2 isotopes analysis for the injected and produced CO2 through pilot producer and nearly producers. The tracer analysis results show clearly the injector from where the injected CO2 has reached the producers. The PLT logs demonstrate good conformance for CO2 and water injection across the horizontal section in the injectors. All these monitoring activities provide a good source of data for further analysis and improved understanding of the pilots. Novel/Additive Information The paper discusses the usefulness of different reservoir monitoring tools for improved understanding of the pilots, which will be used as a basis for implementing CO2 WAG for the full area development.
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