As a young girl, I visited a drilling rig in Naharkatiya, Assam. The drill bit went up and down and procedural instructions had to be shouted to be heard above the din. That was when I first saw a Schlumberger jeep parked alongside and asked what their role was in the drilling operations. I was told that Schlumberger does geophysical well logging. This is done either on a visual inspection of samples brought to the surface (geological logs e.g. cuttings logs, core-logging or petro-physical logging) or on physical measurements made by instruments lowered into the hole (geophysical logs). Important logs include temperature, pressure, gamma, neutron, cement bond log, caliper log, and resistivity. Geophysical well logging is categorized into three main types – open hole logging, cased hole logging and production logging.
A little history
The Assam Oil Company (AOC), a subsidiary of Burmah Oil Company (BOC) drilled its first oil well in Digboi, Assam in 1889. To solve the geological correlation problems of beds, in 1933, the London-based Board of BOC adapted a resolution to bring Schlumberger to Digboi to conduct some electrical surveys. The Digboi well No. 269 was the first well logged by Schlumberger in India in October 1933. By 1934 – 36, it was found that the method identified sand and shale and distribution of oil and water. Within 15 years, Schlumberger’s surveys put correlation into a firm footing, delineating the underground structures and enabling development of the Digboi field. After that, well logging was continued in Digboi by AOC and later in Naharkatiya and Moran by BOC/OIL (Oil India Limited). The Oil and Natural Gas Commission (ONGC) was established in 1956 by the Government of India and the initial well logging was done by the Geological Survey of India (GSI). The departmental logging services were supplemented by contractual logging services of Schlumberger to provide induction/Latero resistivity logs.
Exploring the deep new play and identifying prospects
Schlumberger identified deeper reservoir prospects at subseismic resolution in a structurally complex area with limited well and seismic data using its Petrel E&P software platform.
Recent hydrocarbon shows indicated a deeper prospect, but the deep reservoirs are generally thin, multilayered, and below seismic resolution; making traditional mapping methods ineffective. The basin’s structural—and hence seismic—complexity represents an additional exploration challenge. OIL asked Schlumberger to demonstrate the capabilities of the Petrel E&P software platform for exploring the deep new play and identifying prospects. A pilot project was initiated to establish a workflow in a small field in the basin. The pilot project’s exploration approach in the Petrel platform integrated available data to deliver an advanced interpretation from which geoscientists could rapidly interpret, map, and model from basin to prospect scale. The vital connections of data to interpretation are preserved throughout the assessment into prospect generation. An integrated seismic-to-well-tie study was completed, and Schlumberger experts constructed the seismic-guided model using the Petrel platform’s integrated exploration workflow, which made it possible to understand the heterogeneity of the deeper reservoirs in the upper Assam basin; mitigating the exploration risk posed by the limited well and seismic data for the deeper prospects.
ONGC has signed agreements with Schlumberger Overseas S.A. and Halliburton Offshore Services Inc. for enhancement of production from its matured fields of Geleki in Assam and Kalol in Gujarat, respectively (December 7, 2016) in line with the Hydrocarbon Vision 2030 for Northeast India rolled out by the Ministry of Petroleum and Natural Gas. According to the contract, Schlumberger would make the capital investment, offer technology and services, and receive its reward as a share in the incremental production. Oilex Ltd. has announced the award of two key contracts to Schlumberger and Baker Hughes as part of its 2017 work program at the Cambay PSC (production sharing contract) in India. Schlumberger and Baker Hughes will advise on the optimal well and stimulation design required to achieve potential commercial flow rates.