Improved Oil Recovery by In-fill Drilling in a Mature Field; A Success Story

Abstract

Proposal North Kadi oil field in North Cambay Basin, India has been under production since 1969. The hydrocarbon accumulation in the field is mainly in Middle Miocene sandstone of Kalol Formation having high permeability and strong aquifer support. The development plan of the reservoir had been drawn on the basis of simulation studies carried out at various stages. Recently, remodeling of the field has been done for rational exploitation of the reservoirs. Improved Oil Recovery (IOR) Scheme was formulated after updating the geological model. In-fill drilling of 33 locations were firmed up to achieve the optimal recovery. It envisaged 1.7% additional recovery of in-place oil in 20 years over the primary component of 31.23%. At the time of implementation of the scheme, the field had already produced 20% of 67.0 MMt OIIP. Thirty two IOR locations have been drilled during last three years. As of now, the incremental production from IOR wells is 26% higher than envisaged production profile. The in-fill wells have shown no interference on the performance of nearby wells within their past two years of production history. The drilling and completion cost of the wells break-evened in 20 months. The IOR Scheme involving in-fill drilling rejuvenated the declining trend of a mature oil field. Introduction North Kadi field is a major producer in North Cambay Basin, India. The field was discovered in 1968 and commercial production started since 1969. Hydrocarbon accumulation has been established in multiple pay zones belonging to Early Eocene to Miocene Formations. Middle Eocene sandstone of Kalol Formation is the main producing reservoir having permeability of the order of 500 to 3000 md and strong aquifer support. It holds 95% of in-place oil of North Kadi field. The field development for Kalol pays has been done in phases on the basis of simulation studies. The geological model was build up considering pay sands of Kalol Formation to have a number of layers subdivided on the basis of unit-to-unit correlation for major sand bodies separated by consistent non-reservoir coal/shale in between. Recently, geological model of Kalol reservoirs has been revised by integrating additional petro-physical, core and electro-log data, which indicates that the pay units are not in hydro-dynamic communication. This necessitated to consider each unit as independent entity and hence treated separately for optimum exploitation. The revised classification of the pay units and their mapping has not only helped to resolve the apparent anomalous production behavior of the wells, but also helped in setting the strategy for rational exploitation of the reservoirs. Improved Oil Recovery (IOR) scheme was implemented during the period 2000–2003. Geological Setup Cambay Basin is an intracratonic graben trending NNW-SSE. In northeast, it is flanked by Aravali ridge, on its east and south by Deccan craton. It is bounded on both the sides by basement margin faults. Cambay Basin is divided into four tectonic blocks, namely Ahmedabad-Mehsana, Cambay-Tarapur, Jambusar-Broach and Narmada blocks from north to south (Fig.1).