An Under Balanced Drilling (UBD) pilot project in the Heera and Mumbai High fields of Western offshore India was recently completed successfully. The objective of the project was to establish whether the technology can improve productivity performance in the reservoir section, avoid reservoir damage and thereby enhance oil production from the wells. This paper incorporates the drilling experiences and challenges faced during execution of this pilot project, the well design considerations and methodology, evaluation of the drilling fluid systems and also describes the tangible benefits of using this technology in the drilling of these sections and wells. In terms of the productivity gains from drilling these wells using UBD technology, through the sub-hydrostatic formations offshore Mumbai, the results were very positive. With the success and encouraging results from the pilot project, more wells are now planned, including wells in the losses-prone and depleted Mumbai High and Neelam fields, to incorporate the experiences of the learning curve.
Thapliyal, Anil (Oil and Natural Gas Corporation Ltd.) | Kundu, Sudeb (Oil and Natural Gas Corporation Ltd.) | Chowdhury, Suparna (Oil and Natural Gas Corporation Ltd.) | Singh, Deepika (Oil and Natural Gas Corporation Ltd.) | Singh, Harjinder (Oil and Natural Gas Corporation Ltd.)
Pressure maintenance by gas injection in gas cap is one of the well-established methods for improving the ultimate recovery. Gas injection in the crestal part of reservoir into the primary or secondary gas cap for pressure maintenance is generally used in reservoirs with thick oil columns and good vertical permeability and this process is called gravity drainage. This paper comprises methodology and results of study to evaluate the feasibility of gas injection in gas cap for maintenance of reservoir pressure and to envisage incremental oil gain of a mature offshore carbonate field located in western offshore of India.
Field has already produced more than 30% oil of its initial inplace volume. Water injection was started after 4 years of production and currently field is producing oil with 90% water cut. After one year of initial production phase the field producing GOR rose to two to three fold of its initial value mainly due to contribution of gas from gas cap. Depletion of gas cap gas made significant adverse impact on reservoir pressure and also fast pressure depletion from crestal part had allowed water breakthrough of injection and aquifer water to oil producers. At this stage to reduce the decline rate of wells for maximizing the future recovery without drilling of new wells and also without extension of existing infrastructure, the injection of gas in depleted small gas cap have been studied.
In order to evaluate the feasibility of gas injection in depleted gas cap and its overall impact on oil recovery, three aspects were seen. First the optimized quantity of gas injection and its sensitivity along with the number of gas injectors were decided through reservoir simulation. Therefore, suboptimal oil producers falling within gas cap area are chosen for conversion to Gas injectors. Secondly injection gas requirement for the process will be fulfilled partly through the recycling of produced gas and rest from free gas production from another pay of the same field. Finally it is examined that current existing facility of gas compression will sufficiently cater the additional requirement of gas compression. The process will have additional 10 to 11% contribution in future oil production.
The process of charging gas cap will provide additional support over ongoing water injection leading to a significant additional oil recovery by reducing the oil decline rate.
The Kreuz Glorious has accommodation for 304 people and an eight-point mooring system. It will be deployed for a 2-year project in the Arabian sea for ONGC. Kreuz Subsea and Seamec have successfully completed the mobilization of the Kreuz Glorious vessel as part of a 2-year project with India’s Oil and Natural Gas Corporation (ONGC). The scope of work includes the inspection of 27 offshore jackets in the Mumbai High North, Mumbai High South, Heera, Neelam, and Bassien assets located off the coast of Mumbai in the Arabian Sea. The Kreuz Glorious has a 1200-m2 deck area, with accommodation for 304 people and an eight-point mooring system.
Bartos, Scott Charles (U.S. EPA - Climate Change Div.) | Chakraborty, Ashok Baran (Oil & Natural Gas Corp. Ltd.) | Hauswald, Edward C. (ICF International) | Seastream, Sandy (ICF International) | Shartzer, Andrew (ICF International)
Directly supporting the Global Methane Initiative (GMI), the Natural Gas STAR International Program is a voluntary partnership between the oil and natural gas industry and the United States Environmental Protection Agency (EPA) that promotes use of cost-effective technologies and practices to reduce methane emissions. In 2008 and 2009, the Oil and Natural Gas Corporation LTD (ONGC), the first Natural Gas STAR International Partner in India, undertook a desktop review and in-country methane emissions measurement study and analysis to identify and quantify baseline methane emissions levels for seven of its production, processing and transmission facilities. The measurement study was conducted using infrared camera technology to identify emission sources; and a combination of turbine meters, high volume samplers, and calibrated bagging techniques to measure their emission rates.
This paper details the survey activities and quantitative measurements for the seven surveyed facilities. EPA's Natural Gas STAR International (NGSI) Partners are eligible to receive recommendations on technologies or practices, a facility-specific assessment of their technical feasibility, anticipated methane emission reductions, and the economic and environmental value of the proposed emission reductions. The paper further describes mitigation projects ONGC has deployed as a result of their collaboration with EPA.
ONGC, acting immediately upon the Partnership's recommendations, and consistent with ONGC's corporate carbon management program, have to date reduced methane emissions in the studied facilities by 30 percent, achieving annual natural gas savings of more than 9 million cubic meters (MMcm). This paper also reviews ONGC's future climate protection plans.
ONGC's offshore operations - Application of Floating production systems
ONGC's major share of oil & gas production comes from its offshore fields in water depths ranging upto 100m with facilities mainly confined to fixed wellhead platforms with dry trees, fixed processing platforms and subsea pipelines. This approach is economically viable only for fields having high production potential and long field life, being high capital intensive. ONGC has discovered few offshore marginal fields located at considerable distance from existing processing facilities with peak production potential of the order of 25000 -50,000 BOPD and short production plateau period. Development of these fields with fixed platform and pipeline architecture will not be cost effective. Further Fixed platforms have limitations in terms of water depth and are not suitable for the discovered fields in the deeper waters. Therefore, ONGC started examining the development with alternative technologies like FPSO, MOPU, FSO/FPU combination, etc. for last couple of years.
Each of the alternative solution has its own advantages over the other. Decision to select a particular development option depends on many aspects besides technology and economic viability. The decision has to be weighed on considerations like company's strategy to own asset/facility or to take asset/ facility on hire, operational philosophy (by company itself or hire from contractor), company's experience / position on learning curve for the selected technology. The decision process is necessarily iterative and involves tradeoffs.
The first technology considered for development of a marginal offshore field is by deploying a hired FPSO for processing and export of hydrocarbons. All possible options were examined and weighed against each other wherein hired FPSO approach was found to be most attractive. The exercise carried
out for one field (X) has established that FPSO as a viable alternative for consideration for development of marginal fields offshore. While the contract for hiring FPSO for X field has been awarded and FPSO is expected to be mobilized in Dec 2012, ONGC requires another FPSO for Y field development.
The paper will discuss the Technological & Contractual issues, the acquisition strategy and the lessons learnt in hiring a FPSO for development of marginal fields in western offshore and to master the technologies to regain confidence to operate in deep water in east coast in future.
Ghosh, Arnab (Schlumberger) | Klimentos, Theodore (Schlumberger Asia Services Ltd) | Singh, Rajesh Kumar (Schlumberger Asia Services Ltd) | Nangia, Viraj (Schlumberger) | Malik, Sonia (Schlumberger) | Ghosh, Krishnendu (Oil & Natural Gas Corp. Ltd.) | Bhattacharya, Shyamal (ONGC Ltd.) | Chadha, Harish
The Neelam field is situated in south-east of the giant Mumbai High oilfield in western offshore basin of India. This field was discovered in 1987 and has been put under production since 1990. The field is presently under active water injection and the average oil production from the study area is approximately around
100 BOPD with 95 percent water-cut.
Perforation strategy determination in a brownfield carbonate reservoir under extensive water injection is very challenging. Fluid identification is critical in these reservoirs. Wireline formation tester sampling at defined depths can be very useful for downhole fluid identification. However, the sampling is a stationary measurement and depends on successful communication with the formation fluids. Multi-dimensional nuclear magnetic resonance (NMR) data can efficiently optimize the wireline formation tester operations in such critical wells by using continuous porosity and permeability at various depths of investigations. Additionally, resistivity independent fluid typing and saturation results from NMR analysis at different depths of investigation can be used to optimize the perforation strategy.
Our study established a workflow for designing an efficient completion plan and perforation strategy by integration of multidimensional NMR and formation tester wireline logging technologies in a single acquisition run in the Neelam field. However, the workflow is applicable to similar reservoirs elsewhere in the world. The objective was to enhance oil recovery and reduce water-cut and rig-time. NMR data were used to optimize the formation tester operations by identifying possible tight zones. Moreover, the NMR saturation profiling results provided continuous fluid typing and fluid saturations at different depths of investigations. Formation tester fluid sampling was carried out at discrete station depths in the same run after NMR acquisition; the formation tester station measurements of reservoir mobility and in-situ fluid analysis were then used to validate the continuous NMR log derived fluid characterization and permeability. Based on all this integrated workflow and timely analysis the best possible completion strategy was decided and perforation intervals were optimized. The well is presently producing around 270 BOPD with a 30 percent water-cut.
Heera field is located 70kms south-west of Mumbai city and 140 kms south-east of Mumbai High at an average water depth of about 50m. The field was put on production in November '84. The oil production is mainly from Bassein, Mukta (carbonates) and Panna (basal clastics) formations. The general dip of the field is towards west. The field produced under depletion drive for about six years till Sept. 90. By this time the reservoir pressure dropped to 1300psi from 2150psi and the field experienced sharp decline in production. Water flooding in Bassein formation started in September '90. The production stabilized for some time and then again started declining with a sharp rise in water cut. Current average oil rate from the field is 55,892 bopd with water cut of 56% and GOR 145 v/v through 152 producing strings. The average water injection is 1,36,800 bwpd.
The present study aims to identify injection water breakthrough patterns in the producers of Bassein formation of Heera field. The study area is the upper part of mid- Heera field comprising of wells of platforms HD, HQ, HR and HA. The sudden rise in high water content could be due to the breakthrough of injection water in to the producers. Spider diagrams and contour maps were used to interpret the injection water breakthrough patterns in the study area.
Areal distribution pattern as indicated by contour maps of different ions in the study area suggest that there is more influx of injection water in the wells lying on the rising flank of the basin. In the down dip effect of injection water is less. Wells of HA and HD lying on the eastern side are more affected by influx of injection water than wells of platform HR and HQ.
Continuous withdrawal of hydrocarbon from reservoirs over the years normally results into a decline in the oil production rate with concomitant increase in water cut. Same phenomenon has been observed in the Mumbai High fields. To sustain oil production water injection is normally resorted to for pressure maintenance/reservoir drive. High water cut is one of the reasons for decline in oil production in the fields. Heera field is also experiencing rise in water cut after the start of injection. It is important to know if the rise in water cut is due to injection water breakthrough or some other factors. This is also crucial to know so that necessary steps could be taken to maintain better reservoir health. The study is intended to identify the wells where increase in water cut could be attributed to injection water breakthrough.
Natural tracers are ionic species naturally present both in the formation water and injection water. Prerequisite for a species to be used as natural tracer is the vast difference in the concentration of some of the ions in both the waters. Natural tracer technique 1-3 of identification of the breakthrough involves comparison of the concentration of different ions in the produced water and original formation water (OFW) and Injection /sea water (IW) with respect to the natural tracers like: sulphate, magnesium, strontium, & bicarbonate ions. The concentration of sulphate, magnesium ions and salinity value of IW are more than that of original formation water while the strontium and bicarbonate concentrations of IW are much less than that of OFW. An increase in sulphate and magnesium concentrations combined with a decrease in strontium & and bicarbonate ions concentration indicates the influx of injection sea water into the producers. The results of water analysis of injection and produced water is plotted in spider diagrams and contour maps to understand the extent of influx of injection water in the well as well as the pattern of injection water influx in the study area.