The Importance of Critical Flow Considerations in Understanding Jet Pump Performance: The Mangala Field
Abstract: The Mangala field, located in Rajasthan, India, is characterized by multi-Darcy sandstones, containing waxy and viscous crude oil from which most of the production is being lifted using jet pumps. This is one of the largest applications of hot water jet pumping in the world. The earlier works presented on jet pumping by the operator highlight pump screening, design, monitoring, and operational challenges (Chavan et al-2012 and Singh et al-2013).During the jet pump design work over the years, it was observed th… Show more
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Having the means to efficiently evaluate different forms of artificial lift early in the planning cycle significantly improves the ability to influence other planning decisions (well count, well design, facility capacities etc.) and to realise the potential upsides made available by new artificial lift technologies. Artificial lift screening involves evaluating multiple criteria including rate, well design, cost, reliability, environmental impact, flow assurance, solids handling, operability etc. This paper focusses on a fit-for-purpose methodology to evaluate well production performance for a wide range of artificial lift techniques including Electric Submersible Pumps, Gas Lift, Sucker Rod Pumps, Progressing Cavity Pumps, Jet Pumps, Hydraulic Submersible Pumps and Hydraulic Piston Pumps. The five important attributes of the methodology presented are: Consistency: To ensure a fair comparison is made when evaluating each lift technique, the same assumptions about reservoir performance, fluid properties, multi-phase flow behaviour, geomechanics etc. are used.Auditability: Later in the development planning process, decisions and assumptions will inevitably change, and it is important that there is a proper audit trail regarding how artificial lift screening had been performed to help understand the potential impact of these changes.Efficiency: Early in the field planning cycle, many alternative well counts, well designs and facility configurations will be under evaluation, and assumptions about reservoir and fluid properties will be changing as new data become available. It is therefore important that the artificial lift screening method can be readily applied to accommodate the many scenarios.Technical Rigour: While detailed artificial lift design is not required (or desired) at the screening stage, it is important that the screening methodology applies a fit-for-purpose level of technical rigour to ensure reliable results are achieved and opportunities are not missed through the misapplication of various industry ‘rules of thumb’.Vendor Independence: While sufficient industry research is required to understand the available technologies and new innovations, the screening process should be independent of any particular equipment vendor to prevent any undue bias. The well performance calculations use a nodal analysis approach to develop inflow and outflow curves at the depth of the artificial lift equipment. Then, using knowledge of the fundamental operating principals of the artificial lift techniques, calculations are performed to determine the range of production rates achievable based on constraints including power, flow capacity and gas handling ability. The paper will also present a range of real field cases where these screening calculations have been applied to deep water subsea, onshore conventional and coalbed methane (CBM) developments.
Having the means to efficiently evaluate different forms of artificial lift early in the planning cycle significantly improves the ability to influence other planning decisions (well count, well design, facility capacities etc.) and to realise the potential upsides made available by new artificial lift technologies. Artificial lift screening involves evaluating multiple criteria including rate, well design, cost, reliability, environmental impact, flow assurance, solids handling, operability etc. This paper focusses on a fit-for-purpose methodology to evaluate well production performance for a wide range of artificial lift techniques including Electric Submersible Pumps, Gas Lift, Sucker Rod Pumps, Progressing Cavity Pumps, Jet Pumps, Hydraulic Submersible Pumps and Hydraulic Piston Pumps. The five important attributes of the methodology presented are: Consistency: To ensure a fair comparison is made when evaluating each lift technique, the same assumptions about reservoir performance, fluid properties, multi-phase flow behaviour, geomechanics etc. are used.Auditability: Later in the development planning process, decisions and assumptions will inevitably change, and it is important that there is a proper audit trail regarding how artificial lift screening had been performed to help understand the potential impact of these changes.Efficiency: Early in the field planning cycle, many alternative well counts, well designs and facility configurations will be under evaluation, and assumptions about reservoir and fluid properties will be changing as new data become available. It is therefore important that the artificial lift screening method can be readily applied to accommodate the many scenarios.Technical Rigour: While detailed artificial lift design is not required (or desired) at the screening stage, it is important that the screening methodology applies a fit-for-purpose level of technical rigour to ensure reliable results are achieved and opportunities are not missed through the misapplication of various industry ‘rules of thumb’.Vendor Independence: While sufficient industry research is required to understand the available technologies and new innovations, the screening process should be independent of any particular equipment vendor to prevent any undue bias. The well performance calculations use a nodal analysis approach to develop inflow and outflow curves at the depth of the artificial lift equipment. Then, using knowledge of the fundamental operating principals of the artificial lift techniques, calculations are performed to determine the range of production rates achievable based on constraints including power, flow capacity and gas handling ability. The paper will also present a range of real field cases where these screening calculations have been applied to deep water subsea, onshore conventional and coalbed methane (CBM) developments.
The Mangala oil field in Barmer, Rajasthan is one of the largest onshore fields in India. The field is under an active polymer flood with over 300 wells injecting >400 kbwpd. Jet pumps have been the main mode of artificial lift for the field since production commenced in 2009. The jet pumps are "reverse circulation" type with the power fluid (water), pumped down the annulus. Despite their low efficiency, jet pumps are ideal for Mangala because heated water is used for the circulation fluid which avoids wax deposition in well tubulars. Simple performance curves, often used in commercial packages, work well under two phase liquid only or low GOR conditions. With high gas volume fractions and higher drawdowns, the additional complexity of critical flow is introduced; this occurs when the fluid velocity reaches the speed of sound within the jet pump. These conditions are often encountered in the Mangala pumps, and many jet pump solutions become grossly inaccurate when used for these conditions. A field-wide network model is being used for production optimization; the model employs coupled power fluid and production network systems. Given the size of the power fluid network, an accurate and fast method for jet pump performance under three phase conditions is a prerequisite to the modelling of both well behavior and jet pump sizing. This paper presents a full solution of the fundamental jet pump equations, which are based on Bernoulli’s principle and the conservation of momentum. The method follows the classic solution presented by Cunningham (1970, 1995), which made simplifying assumptions of perfectly incompressible liquids and ideal gases. The proposed technique eliminates these simplifications, making the solution applicable for the situations commonly encountered in the Mangala field. Existing jet pump models for Mangala are based on spreadsheet solutions. These solutions are slow and are practical only for the sizing of individual jet pumps. The new model presented in this paper solves the fundamental equations using numerical techniques and properly accounts for high compressibility fluids, multiphase flow and critical flow. The model was written in Python, which is an object-oriented language well suited to modeling the individual components of the system. The model solves the integrals involved in the revised Cunningham equations, using Newton-Raphson techniques to solve the equations iteratively. The model is used to generate complete (and complex) VLP curves in standard formats which can then be used directly with network models. The new model executes 25-100 times faster than the previous spreadsheet model.
Two Decades of Mangala Field Journey - Key Highlights, Learnings and Recommendations
The Mangala field in India was the first major oil discovery in the Barmer Basin having a STOIIP of nearly 1.3 billion barrels in multiple stacked fluvial reservoirs. It contains medium gravity (20-28 °API), waxy, viscous crude (9-17 cP) in high permeability (1-25 Darcy) clean sandstone reservoirs. The field was discovered in 2004 and brought online in 2009, one of the fastest from discovery to production phase. Hot water injection was started within few months of first production to sweep and maintain pressure. The hot water was essential considering wax appearance temperature (59 degC) close to reservoir temperature (65 degC). The hot water is also used as power fluid for jet pump (main lift system in field) and for annulus circulation in case of shutdown to avoid oil congealing. Jet pump application is the largest in the world with ~160 active wells lifting ~400,000 blpd reservoir liquid with ~500,000 bbls of power fluid. Plateau production of 125k bopd was achieved within 14 months from production start, which is one of the fastest among large onshore fields. The initial average oil rates in wells were ~2000-15000 bopd. Given the high well productivity, the field plateau rate was revised to 150k bopd within a year of achieving 125kbopd. Due to adverse mobility ratio with water, EOR screening and lab study was started right after discovery. Chemical EOR was identified as the most suited with polymer in the first phase followed by surfactant-based flood. Considering the EOR importance, a 5-spot polymer pilot was started almost simultaneously with the start of the field production. Basis pilot results, full-filed polymer flood was started from 2015 which is again one of the fastest EOR implementations. The polymer flood is one of the largest in world with 165 tons/day polymer consumption through ~500000 bwpd of polymerized water injection. Polymer flood reversed the production decline and is expected to give ~8% incremental recovery of STOIIP (~100 MMbbls) by 2030. Following polymer, a successful ASP pilot was conducted in the same wells/pattern which resulted in 20-25% incremental recovery of pilot STOIIP over polymer flood. Planning for large scale ASP implementation is underway. There have been several challenges and important learnings along the way including vertical conformance, areal VRR management, polymer development, degradation, viscosity and quality control over time, jet pump and ESP operations etc. Mangala field recovery has been quite fast with ~37% recovery within 13 years field life. Multiple infill campaigns have been conducted with ~280 wells drilled over 165 base development wells. The paper presents the development journey of Mangala from discovery to date with key achievements, many firsts, learnings and recommendations based on waterflood and polymer flood performance for other similar fields.
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