Increasing Oil Production in a mature field by Rig less Intervention-A MultiWell case study
Authors: Garg Vivek , Ashesh Shubhranshu , Seth Kapil , Govil Amit 
Published: February 2016

Reviving production from brown fields is a major focus of activity for oil and gas companies. This paper outlines the workflow and procedures adopted to increase oil production by rigless intervention from seven wells on an offshore platform of a brown field, located off the west coast of India.

The field under study was discovered in 1987 and put on production in 1994. The main reservoir is Middle Eocene carbonate deposit, which is characterized by the presence of vugs, dissolution channels, fractures (both vertical and horizontal), and hence high permeability streaks that provide conduits for early water breakthrough. This has been primarily responsible for the decline in oil production. The average water cut in the field is 80%.

The offshore platform on which the rigless operations were carried out posed a special challenge due to its proximity to two water injector platforms. The injection water accumulation in the drainage area covered by the wells of this platform became evident through current temperature anomalies and salinity contrast between the formation water and the accumulated injection water (the relevant calculation is explained later in the paper) in the vicinity of the wells taken up for time-lapse survey. Thus, the challenge was to study the flow dynamics so that additional perforations in the bypassed section yield water-free oil and so that very little scope is left for water encroachment even after prolonged production. Open hole logs were studied for locating barriers for injection water. Additional perforations in the bypassed pays were planned taking a composite picture of all facets of data available. The result is the sustenance of incremental production till date. This work has opened new avenues for application to other wells on different platforms. The same methodology with further refinement can bring excellent results in a very cost-effective manner.

The strategy adopted for the project included well diagnostics followed by intervention to increase oil production and reduce the water cut. Production logging was carried out to identify the flow profile. This was followed by pulsed neutron logging where ever required in order to determine the hydrocarbon saturation in the cased hole environment. Integration of data from open hole logs, production logs, and pulsed neutron spectroscopy helped in identifying depleted zones and zones of bypassed oil. Through-tubing isolation plugs (wherever applicable) were placed to isolate water-producing intervals. Oil in bypassed zones was tapped by additional perforations. An innovative approach used to calculate the formation water salinity through pulsed neutron logging allowed the identification of zones of injection water breakthrough. Such intervals were avoided while adding new perforations.

Successful implementation of the above techniques in the seven intervened wells resulted in an increase in the oil production by 53%, i.e, from 1773 bopd (barrel of oil per day) to 2708 bopd. The average water cut of the platform decreased from 80% to 76%.

Candidate Selection

The objective of the operation was to increase oil production while keeping the water and gas production to a minimum. As there was no rig available, the operations had to be carried out on a Modular Skid Unit (MSU), which constrained the available tools and methods.