Multiple Drainhole Wells in an Omani Company
Authors: Wevers Adrian G.P.M. 
Published: December 2007

Multiple Drainhole Technology in drilling and completing wells is widely accepted in PDO as the main opportunity for Unit Technical Cost (UTC) reduction after the successful introduction of horizontal well drilling. PDO's management are committed to an early introduction of the technology because it is recognized that an average of 23% UTC reduction is achievable with this technique. PDO has therefore embarked on a route to introduce this technology in their operations albeit in a step-wise fashion of increasing complexity in order to reduce the risks.

To date sixteen multiple drainhole wells have been executed. The approach to optimize the systems and well designs will be presented. The paper will address the experience in drilling and optimizing the multi-lateral well design, along with the production results achieved to date. Learning points from the initial trials in the Lekhwair field will be addressed first, followed by the successful sequence of water-injector wells in the Saih Rawi field. These wells culminated in the present triple water injector and dual producer combined configuration. Further applications deal with the lining of laterals where a basic design with wire wrapped screens in open hole for sand control has yielded good technical and production results. Plans for a well with cemented liners are in an advanced stage. Future requirements and potential well configurations will conclude the paper.

Introduction

PDO utilizes horizontal drilling technology for the majority of it's development wells and has now embarked on a new technology that will reduce the number of wells required to develop their fields. The new technology is multiple drainhole drilling which is accepted as the next step in reducing Unit Technical Cost (UTC). In this application multiple horizontal drain holes are drilled from a single conduit to surface. The potential scope for this application ranges from replacing several wells with one multi-lateral well with commingled production to dual completed multi-laterals producing different zones separately. Reservoir drainage areas can be increased and inflow patterns optimized, saving surface hole and hookup costs at the same time. The driver for PDO is to use existing assets where vertical wells are converted to multiple horizontal drainholes. No new or additional locations are required and existing assets are utilized more economically. A good example is in the Yibal field development. Reduced economics also make earlier un-economic attic oil available in fields like Amin. The Saih Rawi field is being developed solely by use of multiple drain-holes utilizing water injector and producer multi-lateral pairs.

Project approach:

The first step towards applying this new technology was to establish a scope within PDO and to notify the industry of the requirements. A whole variety of possible wells were identified and a functionality matrix was devised to differentiate between well complexities and functionalities. In multi-disciplinary teams, well candidates were established and best vendors selected based on technical capability and expertise.

Introduction of new technology has to go hand in hand with success. Trials are set up in such a way that risks are minimized to ensure early success. A stepwise introduction of new technology is used to gradually increase complexity and improve equipment and procedures on techniques already used. Early failure of a new technology during trials can cause a set-back of several years before confidence has returned to use the technology. To be able to use this approach a sequence of trial wells are required in order to build on a learning curve. Yard trials and laboratory testing are an integral part of the process.

Once the trial well(s) are completed and the technology is deemed proven. a development pilot period is entered to mature the technology into a final engineered commercial version. P. 481^