The Proper Well Spacings – A Supplementary Method to Maximize The Gulf of Thailand Development Project Value

Abstract

For The Gulf of Thailand (GoT) projects, the bulk of investment goes in drilling development wells and the financial return is depending on how much reserve is effectively tapped by those wells. To improve project economics, both optimizing the well placements to access hydrocarbon and minimizing the number of wells are required. This study shows how proper well spacing used in development well planning is defined using the understanding of reservoir connectivity ratio at a given well spacing. Firstly, reservoir correlation panels of wells drilled within the same trapping fault were created and the reservoir connectivity ratio at a given well spacing were collected. Hence the cross-plot between various well spacing and reservoir connectivity ratio was constructed to establish relationship. New reserves were derived by new pay from the spacing-connectivity relationship and estimated ultimate recovery per metre (EUR/m). With the estimated reserves varied by well spacing, the proper well spacing can be defined by identifying the narrowest well spacing that yield new incremental reserves above economic cut-off. More than 100 cross-plots from Arthit project were conducted by using the existing wells information, the results suggest that a relationship between well spacing and reservoir connectivity ratio is varying depended on trap style, fault strike, channel width & oblique angle and hydrocarbon column height. A new/share pay ratio template is now available to illustrate an expected new/share pay ratio at a given well spacing (ranged from 100 m. to 1,500 m.) in each HC pay unit and subsurface geological trend. From the result, new pay ratio is in the range of 45%-60% at the current well spacing (400 m.) of Arthit Project. Based on the economic justification of Arthit project, there is the opportunity to narrow down well spacing for being economically viable in the future. The optimum well spacing together with an economic viability analysis in each project could be done efficiently. Shortly, the proper given well spacing will be proactively planned for both infill and new wellhead platform. The 2021 infill projects help to validate the current model, improve the prediction function and certainly narrow down those uncertainties for future development projects. Development planning would benefit greatly from proper well spacing so that the optimum number of wells is known upfront so project planning could be properly managed. If tighter well spacing could be applied, more wells could be filled into existing platforms. Then the big investment on new platforms could be deferred. Moreover, this method can be also broadened to other projects where GoT development model can be applied to achieve optimum commerciality.