Agrawal, Nitesh (Cairn Oil & Gas, Vedanta Limited) | Chapman, Tom (Cairn Oil & Gas, Vedanta Limited) | Baid, Rahul (Cairn Oil & Gas, Vedanta Limited) | Singh, Ritesh Kumar (Cairn Oil & Gas, Vedanta Limited) | Shrivastava, Sahil (Cairn Oil & Gas, Vedanta Limited) | Kushwaha, Malay Kumar (Cairn Oil & Gas, Vedanta Limited) | Kolay, Jayabrata (Cairn Oil & Gas, Vedanta Limited) | Ghosh, Priyam (Cairn Oil & Gas, Vedanta Limited) | Das, Joyjit (Cairn Oil & Gas, Vedanta Limited) | Khare, Sameer (Cairn Oil & Gas, Vedanta Limited) | Kumar, Piyush (Cairn Oil & Gas, Vedanta Limited) | Aggarwal, Shubham (Cairn Oil & Gas, Vedanta Limited)
The objective of this paper is to present a suite of diagnostic methods and tools which have been developed to analyse and understand production performance degredation in wells lifted by ESPs in the Mangala field in Rajasthan, India. The Mangala field is one of the world’s largest full field polymer floods, currently injecting some 450kbbl/day of polymerized water, and a significant proportion of production is lifted with ESPs. With polymer breaking through to the producers, productivity and ESP performance in many wells have changed dramatically. We have observed rapidly reducing well productivity indexes (PI), changes to the pumps head/rate curve, increased inlet gas volume fraction (GVF) and reduction in the cooling efficiency of ESP motors from wellbore fluids. The main drivers for the work were to understand whether reduced well rates were a result of reduced PI or a degredation in the ESP pump curve, and whether these are purely down to polymer or combined with other factors, for example reduced reservoir pressure, increasing inlet gas, scale buildup, mechanical wear or pump recirculation.
The methodology adopted for diagnosis was broken in 5 parts – 1) Real time ESP parameter alarm system, 2) Time lapse analysis of production tubing pressure drop, 3) Time lapse analysis of pump head de-rating factor, 4) Time lapse analysis of pump and VFD horse power 5) Dead head and multi choke test data. With this workflow we were able to break down our understanding of production loss into its constituent components, namely well productivitiy, pump head/rate loss or additional tubing pressure drop. It was also possible to further make a data driven asseesment as to the most likely mechanisms leading to ESP head loss (and therefore rate loss), to be further broken own into whether this was due to polymer plugging, mechanical wear, gas volume fraction (GVF) de-rating, partial broken shaft/locked diffusers or holes/recirculation. In some cases a specific mechanism was compounded with an associated impact. For example, in ESPs equipped with an inlet screen, heavy polymer deposition over the screen was resulting in large pressure drops across the screen leading to lower head, but this also resulted in higher GVFs into first few stages of the pump, even though the GVF outside the pump were low, leading to further head loss from gas de-rating of the head curve. With knowledge of the magnitude of production losses from each of the underlying mechanisms, targeted remediation could then be planned.
The well and pump modelling adopted in the workflow utilise standard industry calculations, but the combination of these into highly integrated visual displays combined with time lapse analysis of operating performance, provide a unique solution not seen in commercial software we have screened.
The paper also provides various real field examples of ESP performance deterioration, showing the impact of polymer deposition leading to increased pump hydraulic friction losses, pump mechanical failure and high motor winding temperature. Diagnoses based on the presented workflow have in many cases been verified by inspection reports on failed ESPs. Diagnosis on ESPs that have not failed cannot be definitive, though the results of remediation (eg pump flush) can help to firm up the probable cause.
Khoramfar, Shooka (Texas A&M University-Kingsville) | Jones, Kim (Texas A&M University-Kingsville) | Boswell, James (Boswell Environmental) | Shah, Aditya (Texas A&M University-Kingsville) | Aggarwal, Shubham (Texas A&M University-Kingsville) | Ghobadi, Jalil (Texas A&M University-Kingsville)
Volatile organic compounds (VOCs) present in crude oil can be released to the atmosphere from storage tanks, wastewaters and equipment leaks in petroleum industries. A pilot-scale sequential biotrickling-biofiltration (BTF-BF) unit as an environmentally safe and economical treatment procedure was designed and tested for removal of VOCs from a wastewater sump at the CITGO Corpus Christi Refinery. To identify and quantify VOC emissions from the refinery wastewater sump, the air was sampled using 6 L canisters and characterized using gas chromatography-mass spectrometry. The pilot-scale unit included a BTF for removal of more water soluble compounds followed by a BF for removal of poorly soluble compounds. Performance of the BTF and BF units containing plastic cross flow and compost-based media were investigated at pollutant loading rates of 6 g/m3hr to 1750 g/m3hr.
The characterization results of the pilot test showed benzene as the main constituent of the vapor stream (85% of vapor) emitted from the wastewater sump. The ratio of benzene to toluene and xylene was determined to be 12:2:1 in these samples. The high concentration of benzene as an amenable food and energy source for the microorganisms lead to high biomass growth and more than 85% removal efficiency (RE) for total emitted VOCs.
Application of an innovative sequential biotrickling-biofiltration unit was also demonstrated to effectively handle the cyclic emissions of VOCs at most oil and gas industries. Although several researches have been done to evaluate the performance of BFs and/or BTFs in the laboratory, this pilot study can be used to design and optimize the performance of a bio-oxidation unit under actual refinery operating conditions.
Bhagyam field is an onshore, shallow field containing light sweet oil (270 API) with low Gas Oil Ratio (GOR) (~100 scf/stb). The crude has ~30% wax content with moderate insitu oil viscosity of ~ 50-250 centipoise (cP) with wax appearance temperature (WAT) ~2o C lower than the reservoir temperature of 530 C. With water production, it was initially expected that viscosity of production fluid will rise upto 3000 cP due to emulsification.
Rod driven Progressing Cavity Pump (PCP) system was selected as artificial lift for the field development considering low GOR and relatively high fluid viscosity. To ensure flow assurance of the high WAT crude, various methods such as annular hot water circulation, heater cable, vacuum insulated tubing (VIT) etc were considered. Based on the analogue Mangala field, which is located in the same license area, it was decided to utilize annular hot water circulation as the downhole heating methodology as it provided a significant completion design similarity with previous installation and operational experience. This completion involves running Colied Tubing (CT) clamped to the main production tubing as a secondary string. The main production tubing with PCP stator is stabbed in a production packer for downhole isolation.Hot water is circulated at 850 C down the coil taking returns through the annulus. This arrangement ensures temperature of the fluid inside the main production tubing is maintained higher than the WAT at all times.
In the 1st phase of field development, wells completed with PCP and have been successfully operating for ~ 2 years meeting requirement of flow assurance & PCP run life. However, PCP efficiency was lower in high GOR wells, as downhole gas separation was not possible. For the 2nd phase of development, alternate completion designs which can mitigate the downhole flow assurance challenges and at the same time open up the annulus similar to a conventional PCP application were considered and finally hollow rod driven PCP design was selected as the most suitable method.
The paper details PCP application in Bhagyam field during the first two phases of development, installation & operating practices, lessons learnt & overall system performance.