Technologies such as time-lapse seismic (4D) and advanced spectral decomposition can help produce additional oil and gas, extending the economic life of our fields
Imagine the quality of life today if the mobile and internet technologies had been used as widely in India during 1960s as they are being used today. Exploring sedimentary basins for oil and gas is a long process of elimination. Based on data gathered, one eliminates areas where conditions for accumulation of oil and gas did not exist, to zero in on areas where conditions existed, of course millions of years ago. To gather geotechnical data, deploying latest technology and tools are critical.
What were the technology and tools India used during the 1960s to explore for oil and gas? I asked a good old geologist, who served ONGC for over 30 years, and this is what he said, “those were the days when western countries remained completely indifferent and unsupportive. The only country that extended support to our oil and gas exploration efforts was former Soviet Union and the tools we had to use were naturally outdated even then.”
During the 1970s, three-dimensional (3D) seismic surveys entered the oil and gas sector with a big bang and changed it forever. This one technology doubled the Probability of Success (PoS) in exploration, decreasing the risk significantly. It opened up global offshore exploration in a big way.
Offshore seismic survey triggers an artificial seismic event (small earthquake). A survey vessel (ship) towing a network of cables usually employs airguns to release compressed air pulses into the seawater which travel to the sea floor. Seismic energy so generated in the form of sound waves pierce through the water column and formations of the earth’s outer surface. Later, it reflects back to the surface of the water where it is recorded by a set of hydrophones. The reflected sound waves convey information about the terrain’s structure. Collected data is then analysed to construct a 3D image of the subsurface. This 3D image aids a geologist in the same way an ultra-sound image aids a physician.
Appreciating the importance of 3D seismic surveys to the success of offshore hydrocarbon exploration, several countries acquire wealth of multi-client seismic data and provide easy data access to international energy companies to attract risk investment. But these best practices are yet to be adapted by India.
One of the oil and gas fields in India where application of best-in-class discovery and recovery technologies have paid rich dividends is the Ravva oil and gas field. The word ravva in Telugu means diamond; the field, discovered in 1987 and brought into production in 1993, has so far produced over 250 million barrels of oil and 300 billion cubic feet of gas, more than double its initial estimates. In today’s prices, that is cumulatively worth over R1,50,000 crore ($25 billion).
Staged and appropriate use of geophysical technologies and multi-disciplinary integration has helped in extending the life of this field. As a result, Ravva oil and gas field is set to achieve a recovery rate more than 50%, while the average for other fields in India is less than 35%. This will be a unique distinction that India needs to be proud of. Let us look at just two technologies applied that made a difference and added significant value to all the stakeholders.
Time-lapse seismic (4D) technology
4D seismic is an advanced method of acquiring, processing and interpreting repeated 3D seismic surveys at different time stamps. 4D technology brings fourth dimension (time) for identifying areas of bypassed oil reserves. A 4D OBC seismic survey was carefully planned, executed and interpreted on the Ravva field, first time in India. This was achieved with the systematic implementation of a 4D workflow from feasibility study to the multi-disciplinary interpretation in order to identify the unswept oil and gas pools. The 4D seismic technology also helped in optimisation of reservoir management plan and in placing the new infill wells successfully.
Advanced spectral decomposition technology
Ravva main reservoirs middle miocene are overlaid by thin late miocene reservoirs. These are thin and isolated reservoirs that are difficult to map using conventional seismic interpretation methods. Spectral decomposition is an invaluable tool for imaging and mapping thin bed reservoirs and revealing seismic geomorphology. This technology was applied in Ravva and attributes at different frequencies computed, co-blended and visualised using advanced 3D visualisation environment to highlight the thin channels and their geometries. These channels were subsequently drilled as secondary targets in the infill drilling campaigns to achieve incremental production.
The objective behind deploying these technologies is to identify bypassed oil and gas pools and thin isolated oil and gas filled channels in order to drill and produce them so that the economic life of the field gets extended.
Over the last 10 years, India could drill on an average less than 600 wells in a year, against over 20,000 wells being drilled very year in Canada alone, and there are more than million wells on production in the US. While the Indian sedimentary basins spread across a 35 lakh sq km area, 3D seismic surveys have so far been conducted in less than 15% of the area only and 4D seismic survey has been done only in Ravva. Interestingly, out of the total of 5 lakh sq km area covered by 3D, more than 50% has been carried out post the entry of private players into the sector.
India has over 450 oil and gas producing fields, some of them commenced first production during the 1960s when none of the above technologies existed. But today they are available and have been successfully deployed in multiple fields around the world.
The questions to be asked and answered are: (1) Why the exploration activity in the country is so low? (2) Why is there a reluctance to deploy proven discovery and recovery technologies? (3) How much funds are being allotted for R&D in upstream oil and gas sector that holds the potential to transform the country?
India holds over 750 million metric tonnes of oil and over 1,300 billion cubic metres of gas reserves. Imagine the benefits to the country if these technologies could be deployed across all the appropriate producing fields to improve the recovery factor by a modest 5%. Such an increase in the recovery rate would enable us to produce additional oil that would be slightly more than the current annual domestic oil production.
Source: FE
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