Successful Application of Cluster Drilling Concept to Reduce Cost and Increase Profitability in a Mature Onshore Gas Field in East Kalimantan
Authors: Hazman Harry Alam , Wijanarko Andre , Kurniyati Umi , Prihartono Yoseph A. , Prihandono Bambang , Ianiro Antonio R. , Narayanan Ram K. , Schmohr Donn , Rylance Martin 
Published: October 2008

Abstract
Several development strategies are currently being evaluated and applied by VICO, in order to increase the near term production rate and maximize recovery from the existing fields, within the Sanga-Sanga PSC, East-Kalimantan, Indonesia. This paper will focus on the "Cluster" drilling concept; that has been successfully applied within the Nilam field, which is the second largest field within the PSC.
A combination of a complex fluvial-deltaic depositional environment, along with increasing development costs and reservoir uncertainty due to advancing field maturity, has driven the VICO development Team to re-evaluate the drilling and completion techniques being utilised in order to access the remaining hydrocarbon resources within the field. This re-consideration has allowed a number of novel and alternative solutions to the problems to be proposed, one of these solutions has been the "Cluster" well approach.
The principal objectives of the "Cluster" approach are, to reduce the unit gas development costs, increase the short-term production rate and maximize the cumulative recoverable gas volumes from the field. Well cost reductions are being achieved through improved rig utilization and by the drilling of multiple wells from a single pad location. A dramatic increase in the short-term rates is being achieved through drilling dedicated wells to produce the shallow, higher permeability reservoirs. Finally, the recoverable reserves from the deeper, lower permeability reservoirs, which typically produce at lower rates but have a longer effective production life; are also being maximized through the application of dedicated completions (via the Dual Monobore concept).
This paper will discuss the "Cluster" concept in detail, in brief a "Cluster" consists of the drilling of a "Mother" well which is then used as a reference well to acquire a full suite of open-hole data, this data is then processed in order to assess and define the opportunities within the immediate ‘local’ area of interest. The "Mother" well is then followed by the drilling 1, 2 or more "Daughter" wells from the same pad; the exact number of these "Daughter" wells being determined by the quality, quantity and type of information that is made available from the "Mother" well logs and tests. These additional wells were initially being drilled on twenty-foot centres, and the "Daughter" wells are typically constructed with some form of slim-hole approach, with minimal associated data acquisition in order to reduce the overall costs.
This paper will present the results from the two sets of complete "Cluster" wells competed to date, within the Nilam field; and will provide a brief description of a third "Cluster" group that is currently being finished. The application of this technique has resulted in an average reduction in the well costs of more than 20% and a much improved set of well economics in both the short- and long- term; compared to drilling a single conventional well from a pad. The paper will also discuss the current candidate selection process, "Cluster" well design and header configuration, the drilling operations themselves and the subsequent post well evaluation.