An Overview of Re-Entry and Clamp-on Infill Drilling for Incremental Recovery in Offshore Field

Abstract

Bombay high is a highly heterogeneous, multi-layered carbonate reservoir overlain by gascap and underlain by aquifer in Western continental shelf of India and is in mature stage of its producing life. The field is currently undergoing "Mid-life Crisis", necessitating major re-development and well interventions programs for stemming the decline in oil and gas production and maximization of recovery. Being an offshore field, sidetracking (LDST, MDST and SDST) of existing wells and drilling of infill wells through clamp-on have become sort of immediate preferred cost-effective option in Bombay High; firstly, for sustained oil production and commensurating the water injection and secondly for facilitating the additional recovery of bypassed, un-swept/less-depleted reserves. Failures/limited success of repetitive workover jobs, poor cementation, bad wellbore condition, early water breakthrough have made many wells susceptible to channeling behind casing and cross flow between the layers. Relocation of such wells and utilization of slot have become inevitable. Sidetracking is being practiced, as a measure for reducing the inventory of sick wells where all the conventional remedial measures have not met with desired results and have also limited the further scope of rectification. This paper deals with the selection criteria, implementation and analysis of techno-economic successes and failures of re-entry/re-engineering of sub-optimal/uneconomical and clamp-on infill wells and also summarizes what has been learnt over the past several years and future scope of such activities. INTRODUCTION The Bombay High Field located nearly 160 Km W-NW of Bombay (Now Known as Mumbai) city in Arabian Sea was discovered in 1974. The field holds 1724 MMt and 389 BCM of initial in-place oil and gas respectively. The field was put on commercial production in 1976. The field production peaked around 19.5 MMTA during 1984–85 and maintained the same production level for about 7 years. Thereafter production started declining and reached to the level of about 10MMTPA at present During last few years the field is engulfed by typical oil field problems like high water cut, high GOR, differential depletion, water breakthrough and aging of facilities. All out efforts are being made to arrest the decline through massive well intervention programs and also by drilling new infill development wells. Drilling of new infill wells by installing the clamp-on on the existing platforms where no free slots are available and also by sidetracking the problematic existing wells have been preferred to step up the production and to drain the bypassed oil. The present paper discusses about selection, implementation and success/failure of these two techniques practiced in the Bombay High field.

Optimizing the Development Concept of a Mature Gas Field in Intensive Drilling Context: Tunu Field Case

“…2 Tunu field is today produced in MP mode with LP compression planned for third quarter of 2009 and Low Low Pressure (LLP) in 2014. Feedback from other operators demonstrates application of this technique for mature field redevelopment with a high probability of success (75-80%).…”

“…Gas bearing reservoirs are found in the Tunu Main Zone (2,,000 m depth), representing sequences of thick shale and thin sand bodies, deposited in the delta front of the successive Mahakam deltas during the upper Miocene period. Tunu reservoirs consist of bars and channels randomly distributed both laterally and vertically.…”

Stepping on Development of Small and Medium Size Oilfields through Horizontal Wells—The Way Ahead

“…Following types of wells are considered for sidetracking: 13 • The wells which have mechanical problem like casing leakage, tubing rupture and fish, corrosion etc • The wells workedover several times for water control and have no expected gain with further workover • Development/infill wells which have encountered poor/less pay especially in periphery • Poor/suboptimal producers at present location and have scope for better production at nearby subsurface locale • Optimization of well spacing by sidetracking as a substitute to infill wells • Converting poor producers into injector after relocating by sidetracking • Sidetracking due to drilling problem • Revival of sick/abandoned wells which have produced large amount of oil from most of the available layers at present location and repair of sickness at present location is not possible • Placement of location with additional drift in order to increase the drainage radius • Drain hole drilling from existing well to tight reservoirs/ layers Main advantage of sidetracking is revival of chronically sick or dry wells, which are unlikely to give success through low cost workover. This also reduces the lead-time required for the preparation of drilling of new wells both in onshore and offshore environment.…”