After the success of a pilot project, Cairn India Ltd. has taken up a US $600 million polymer flood EOR project for Mangala field in RJ-ON-91/1 block in Rajasthan, western India, to enhance crude oil recovery.
“With strategic focus on increasing ultimate recovery from operating fields, we have commenced execution of [the] polymer flood EOR project at Mangala,” said Cairn India CEO P Elango. “Major contracts for the execution are being awarded and polymer injection is expected to commence by Q4 FY15 (January-March 2015).”
The Mangala field was chosen for the project just six years after its first production due to its unfavorable geophysical characters. Oil in the Mangala ground reservoirs is waxy and viscous (7-20 centipoise). The higher viscosity of oil compared to that of water makes lower sweep and oil displacement in the ground reservoirs, resulting in less recovery of oil from wells.
The field produces about 150,000 b/d despite the presence of about 1 Bboe in reserve. Actual oil recovery from this field is around 13% of Stock Tank Oil Initially In-Place (STOIIP) till now.
The main reservoir in Mangala is the Fatehgarh Group, consisting of interbedded sands and shales. It is divided into the Lower Fatehgarh formation dominated by well-connected sheetflood and braided channel sands, and the Upper Fatehgarh formation dominated by sinuous, meandering, fluvial channel sands. Five reservoir units (FM1-FM5) have been identified.
Oil production in Mangala has reached its peak, according to an internal study, and production will start falling from early or mid 2014 if the EOR is not implemented.
EOR Project
The operator is implementing the EOR scheme with alkali surfactant polymer (ASP) flooding in Mangala field wells to maintain a plateau production rate over a longer period and to increase the ultimate oil recovery.
The EOR scheme involves drilling of a total of 141new wells – including 117 injectors and 24 producers – in the Fatehgarh Mangala (FM1) area, use of existing wells for a closely spaced pattern of polymer injection, setting up a central chemical processing facility for preparation of SAP, and in-field pipelines for distribution to EOR well pads in Mangala field.
Engineers India Ltd. has been awarded a contract to design additional surface facilities for 15 existing well pads with associated pipelines and infrastructure facilities for the EOR project.
A pilot project has established the efficacy of polymer flooding by improving recovery and reducing water cut. The experiments indicated that aqueous-based chemical flooding EOR processes are the most suitable for Mangala field, considering its rock and fluid characteristics.
With the addition oilfield polymers, it is possible to make injection water just as viscous as oil and minimize its tendency to “finger” through the oil. This polymerized water displaces more oil and increase sweep efficiency. The use of alkali and surfactant chemicals-based injected water acts almost as soap and extracts more oil from the reservoir rock surface, resulting in increased displacement efficiency.
ASP flooding is the most effective process for Mangala field, with an incremental oil recovery of more than 30% of STOIIP, while a basic mobility-control polymer flood showed an incremental recovery of about 15% of STOIIP.
The EOR project is expected to improve oil recovery to 32.1% of the STOIIP, from 13% at present, and yield an incremental production of 70 MMbbl by the end of the PSC in May 2020.
After this, the cumulative oil production from the Mangala field is expected to increase from 246 MMbbl to 334.5 MMbbl.
“We are excited about the Mangala polymer flood-based EOR program for enhancing ultimate recovery, and are working on plans to extend the program to other fields in future,” Elango added.
Cairn India intends to implement chemical flooding in Bhagyam and Aishwariya fields, located adjacent to Mangala, in the second phase.
New Discoveries
Besides the EOR plan, Cairn India continues to take up exploration and development work in producing and prospective fields in Rajasthan block.
“The renewed exploration and appraisal program during 2013 resulted in three discoveries in Rajasthan,” the CEO said. So far, these three new finds have increased the total discoveries in Rajasthan block to 29.
The Aishwariya 4-Z discovery in Barmer Hill formation area, the block's 27th discovery, pumped out oil at a rate of 450 b/d on testing, confirming further potential for hydrocarbons in the formation. The 28th discovery, V2Y Channel, opened up multiple pay zones in low permeability Barmer Hill formation in the eastern margin of the basin. This one flowed oil at about 450 b/d from three zones after fracking.
The operator claims that the new finds are estimated to add 500 MMbbl to 600 MMbbl of oil in place resources to the existing resource base of 4.2 Bboe.
A new 3-D seismic data survey has been launched to acquire data from more than 1,900 sq km (734 sq miles) in the Rajastan block to identify new exploration leads and augmenting the prospective resource base.
In producing fields, Cairn has a plan to drill 48 infill wells in the Managala field to support the plateau production of 150,000 b/d in one to two years. These infill wells will be converted as injectors later to support the EOR project. It would drill 72 new infill wells in Bahgyam and Aishwarya fields
A development plan for the Barmer Hill formation has been prepared. It will utilize fracture stimulation and horizontal well completion technology to monetize the low permeability resource in the Barmer Hill zone. Development plans also have been submitted for two other satellite discoveries in the block – NI and NE fields.
Elango earlier said that his company planned “to drill in excess of 450 wells in the Rajasthan block over a three year period, including 100 exploration and appraisal wells and the balance as development wells to sustain and enhance production volumes.”
The five oil producing fields – Mangala, Aishwariya, Saraswati, Raageshwari, and Bhagyam – and the Raageshwari Deep gas field in Rajasthan block jointly produce about 184,900 b/d of oil and 8 MMcf/d of gas.
The Rajasthan block in the Thar desert in Rajasthan is estimated to contain about 7.3 Bboe, with a discovered resource base of approximately 4.2 Bboe and prospective resource base estimated as 3.1 Bboe.