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Gupta, M K (Oil and Natural Gas Corporation Ltd) | Sukanandan, J N (Oil and Natural Gas Corporation Ltd) | Singh, V K (Oil and Natural Gas Corporation Ltd) | Pawar, A S (Oil and Natural Gas Corporation Ltd) | Deuri, BUDHIN (Oil and Natural Gas Corporation Ltd)
In an offshore field, mitigation of H2S from natural gas itself is a big challenge. A situation where high H2S present in well fluid increases the challenges several fold to sweet both processed oil and gas. In a wellhead platform/remote location where manual intervention requirement is minimal, conventional process has several limitation such as space availability, load on structure, frequent monitoring etc., hence may not be suitable for mitigation of H2S from processed gas and oil.
In this work, an approach is adopted for sweetening of sour gas and sour crude in an optimum way, keeping offshore constraints in mind and without usage of rotating equipment's. An integrated simulation model is developed in Aspen HYSYS process simulator wherein well fluid from well manifold is processed in three phase oil and gas separator. The gas liberated from the separator is first sweetened in adsorption columns considering three bed systems unlike general usage of two. The oil is sweetened in an envisaged stripper column utilizing sweet gas from adsorption column as stripping gas. In this work, a three bed adsorption column is envisaged wherein 1st two column in used for sweetening of gas liberated from separator which consists of around 7500ppm H2S. Sour oil from the separator which contains around 2000 ppm of dissolved H2S is processed in a stripper column for mitigation of H2S dissolved in the oil. Sweet gas liberated from 1st two column of adsorber bed is used as stripping gas for oil sweetening. H2S liberated from stripper column is routed to the 3rd column for sweetening. After this gas from all the adsorber column is combined and routed to process platform along with the sweet oil. Analysis reveals that, this scheme can sweeten altogether both oil and gas to the desired H2S level without the need of any rotating equipment's and must be a suitable for remote location.
A holistic approach was taken for sweetening of oil and gas without the need of any rotating equipment's, & any chemicals, unlike the conventional method and hence can be suitably adopted for an offshore environment or at remote location where requirement of manual intervention is bare minimum.
The relentless exploitation of hydrocarbon resources to meet ever increasing demand has compelled upstream companies to focus on deep and ultra-deepwater. Flow assurance is one of the most critical aspects in field development. The hydrocarbon product needs to be transported from a remote well to the process facility, without experiencing significant energy losses to the environment. Some of the oil discoveries in Indian deepwater are having high wax content; high Wax Appearance Temperature (WAT) and pour point flow assurance is a major challenge in low ambient temperatures.
A number of solutions like chemical injection (CI), mechanical insulation (Vacuum Insulated Tubing (VIT), Pipe-in-Pipe (PIP) etc.), Pigging, Piggy back line (PBL) and Electrical heating of flowline (EHFL) are the available means of mitigation to address these flow assurance challenges. In addition to high ‘steady state’ thermal insulation performance, the system has to provide good transient cool down behavior to prevent wax or hydrate formation during shut down and to minimize the time required for start-up. Through this paper an attempt has been made to generate a matrix for identifying the likely option for the means of mitigation individually or in combination, both for steady state and transient scenarios.
The various options have been studied for suitability for flowline under different flow scenarios like steady state, shutdown, restart, and turndown and for redundancy. Emerging options are further technically analyzed qualitatively, based on the extent of field use, robustness, tangible & intangible benefits etc. and evaluated to arrive at a suitable flow assurance strategy. For field X located in 600–700 meters of water depth, the combination of PIP and CI with EHFL as a fall back is emerging as the most suitable option. During initial start-up, the flowline can be preheated using electrical heating and the sample taken for identification of suitable inhibitors and for arriving at the required dosage. During shutdown and restart scenarios electrical heating of flowlines can be adopted to prevent the fluid from gelling.
The solution matrix presented in this paper will help in evaluating the available options and to arrive at the best suitable flow assurance strategy and means of mitigation, to any field during all operating scenarios.
Medavarapu, Kishorekumar (Oil & Natural Gas Corp. Ltd.) | Mahato, P.K. (Oil and Natural Gas Corporation Ltd) | Das, Santanu (Oil & Natural Gas Corp. Ltd.) | Singh, Sureshkumar (Oil & Natural Gas Corp. Ltd.) | Patel, Kantilal C. (Oil & Natural Gas Corp. Ltd.) | Nandan, Alok (Oil & Natural Gas Corp. Ltd.)
Customized hydraulic fracturing operations in low temperature and shallow reservoirs of Gamij field of western onshore India yielded impressive post frac production gains. This paper describes in detail, the various challenges for hydraulic fracturing in Gamij field, development of fracturing fluid, execution methodology and fracturing's vital role in production enhancement.
Successful hydraulic fracturing operations turned Gamij as one of the promising producing field. Poor reservoir characteristics, thin pay zones, presence of coal layers, shallow depths and low reservoir temperatures were the main challenges for hydraulic fracturing. Numerous lab studies carried out and fracturing fluids were customized for good rheological capabilities and post-frac gel cleanups. Frac job sizes were optimized based on sensitivity analysis carried out using frac simulators. Large size jobs were carried out in suitable candidate wells. Pre and Post frac temperature logs were taken to ascertain the fluid intake and frac confinements. Activation methodologies developed so as to bring the wells on production in minimum time.
Hydraulic fracturing jobs in Gamij field were quite successful. Fracturing jobs were carried out in 35 wells in the last two years mostly with drilling rig in position. Most of the wells came on self. Oil production up to 30m3/d in a single well was observed. Job sizes were designed based on reservoir characteristics which ranged from 60000 lb to 242500 lb. 20/40 low strength proppant pumped in these frac jobs with maximum concentration of 15 ppg. Job scheduling varied based on thickness of payzones, behavior of nearby coal layers. Temperature logs showed a good placement of proppant in target zones which helped in getting impressive post frac productions. The results of frac jobs turned this small field into one of the most promising fields in the area.
Customized hydraulic fracturing helped in the enhancing the production from ageing & mature western onshore oil fields of India. Success of fracturing campaign in Gamij field led to augmented drilling activity in similar pay zones to extract hydrocarbons and support the increasing energy demand. This strategic hydraulic fracturing methodology customized for other fields in the region which were also proved quite successful.
Bahukhandi, Yogesh (Oil and Natural Gas Corporation Ltd) | Kar, Somenath (Schlumberger Asia Services Ltd) | Majumdar, Chandan (Schlumberger) | Roy, Dipanka Behari (Oil and Natural Gas Corporation Ltd) | Bhatt, U.C.
Heera field is one of the most prolific fields in the Mumbai offshore basin in India. The field belongs to one of the six tectonic blocks (Heera-Panna-Basseinn block) of Mumbai offshore basin. Carbonates are by far the major contributor in terms of hydrocarbon production in this field. Presence of Vugs, Fractures and Solution enhanced features makes it a real challenging job to understand the porosity distribution within this reservoir. Characterizing and quantifying the complex secondary porosity profile and identifying different flow unit is immensely important for production optimization and appropriate completion design. The challenge of understanding the porosity heterogeneity of Carbonate reservoir further increases where critical borehole condition averts the possibility of running high resolution Wireline imaging tool.
A novel approach has been taken for the first time in this field to quantify and characterize the secondary porosity distribution and permeability prediction from high resolution LWD Resistivity Image. Good quality LWD Resistivity Image has been processed using advance processing software and a quantified result of secondary porosity spectrum was obtained using robust algorithm. This quantified secondary porosity result is further utilized to characterize the different high resolution flow unit throughout the borehole.
This paper illustrates a case study where quantified result of secondary porosity and estimated permeability has been derived using LWD resistivity image in conjunction with the openhole measurements.Micro-facies variation in terms of fluid flow characterization, size & nature of vugs and laminated beds has been established. This will lead to accurate completion designing for production optimization. The result was then validated with the secondary porosity derived from the high resolution Wireline Image and Mobility data from samplingtool.
In a nutshell, this work opens a new regime of application of LWD image in terms of advance Geological and Petrophysical interpretation in addition to its other benefits like borehole stability and Geosteering capability.
Chandola, S.K. (Oil and Natural Gas Corporation Ltd) | Singh, V. (Oil and Natural Gas Corporation Ltd) | Singh, J.N. (Oil and Natural Gas Corporation Ltd) | Chaturvedi, R.K. (Oil and Natural Gas Corporation Ltd)
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