Utility of Seismic in Deciphering the Reservoir Contact in Horizontal Wells - A Case Study in Mumbai High Field

Arvind K. Nauriyal, Ajoy Sarkar, V. Kamat, and Bvrrk Murthy
MH ASSET, ONGC, Mumbai, India

The ever increasing demand for hydrocarbons and huge strikes of oil becoming a rarity, the geoscientists and production engineers were prompted to tap that oil which was left un-recovered as bypass and residual oil in the already producing and mature fields. Failure to understand the reservoir geometry and the fluid content while modeling a horizontal well may lead to costly mistake, which can be avoided by an insight into the seismic data and its attributes. As the normal seismic signatures fail to give a meaningful intra bed configuration in terms of lithofacies, geo-scientists look for more appropriate method of identifying the rock character. Rock lithology, porosity and saturation are interrelated to the elasticity of the seismic signatures and the relation can be obtained from acoustic impedance in terms of varied facies.The use of acoustic impedance in discriminating the good facies from un-favorable facies is an easy method commonly practiced in the industry as it allows the placement of horizontal wells in thin beds to the most possible appropriate path. Especially in the offshore drilling where enormous cost of drilling is involved, accurate placement of horizontal wells is of paramount important.Authors carried out the post stack inversion of the seismic data taking into consideration the well data on the Mumbai High field, in the western offshore basin of India. The acoustic impedance so generated has been freely used to locate the producing facies in the reservoir with the help of an analogical study/calibration of the producing wells in the area. The absolute amplitude attribute of the seismic data has also been taken into consideration to substantiate the seismic inversion data. A number of wells are released and the horizontal well paths are designed accordingly on the basis of the combined study of absolute amplitude and acoustic impedance. The study guided the well path when under drilling and the chances of deviating from the desired reservoir facies were reduced to minimum.

The case study deals with a current well under drilling and in the paper authors discussed the method so adopted that met with an amazing success in the placement of the horizontal wells in the Mumbai High field and suggested that seismic inversion should be adopted as an integral part of interpretation to predict favorable/producing facies in the development of a proven hydrocarbon bearing field.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery