Managing Subsurface Uncertainty during the Successful Development Drilling of the Hides Gas Field
The Hides Gas Field is located within the Hela Province of the Papua New Guinea (PNG) Highlands and underpins the PNG LNG project. The Hides surface anticline is characterized by its size – measuring over 40km in length and climbing to 2805m in elevation it dominates the surrounding landscape. The outcropping geology is also spectacular, with weathering of the Miocene age Darai Limestone creating a rugged terrain with significant karst topography. However these geological features, while impressive, made it challenging to obtain data and define the resource size of the gas field, with the acquisition of seismic data particularly affected by the difficult operating environment. Additionally, the initial appraisal wells (drilled from 1987 to 1998) did not intersect a hydrocarbon-water contact, and together with the significant structural uncertainty this led to a wide range in the possible static assessment of the resource. Subsequently, additional data were required in order to prove commerciality and proceed to development. Commencing in 1991 low rate production from Hides 1 and 2 was utilised for a Gas to Electricity plant. Upon drilling of Hides 4, pressure data showed reservoir depletion and a downhole gauge exhibited interference as a result of this production. Analysis of these data reduced the range of resource size uncertainty and were sufficient to underpin the external reserve certification required for sales contracts and financing, and allow the decision to proceed to development. For development the LNG project required 9 high deliverability gas wells at Hides (>200 mscf/d). Due to the persisting structural uncertainty the location of the development wells was critical. The primary objective was to ensure deliverability and maximize condensate yield, while it was also recognized that there was a need to continue appraisal of the structural form and reservoir connectivity and properties. To achieve these objectives the wells were planned to be drilled in crestal locations and largely within existing well control, with multiple datasets acquired while drilling to assist with well landing and further delineation of the field. Following development drilling, in terms of the connectivity and properties of the reservoir the results were largely consistent with pre drill predictions, with the major sandstone intervals displaying log properties of similar quality to that observed from the initial appraisal wells. Conversely, the drilling results revealed a structural form not predicted by the pre drill seismic interpretation and structural modelling. This was particularly evident in the NW area of the field at Well Pad G where two wells were drilled outside well control. In this region the seismic data was of particularly low quality, and as such multiple different structural models were developed prior to drilling. The first well, Hides G1, encountered formation dips in-line with the predrill prediction however top reservoir was intersected 400m high to prognosis. The second well from the pad, Hides G2, drilled a an over-thickened intermediate hole section with consistent but extended log character. Through the acquisition of high-quality formation dip data it was revealed that a sub-vertical panel of strata had been intersected, pushing the reservoir over 600m deeper than the pre-drill prediction in that location. Subsequently the well was re-oriented to the SW at a high inclination build-rate, with the revised trajectory successfully intersecting a vertical reservoir section. The Hides development drilling campaign overcame the dual challenges of remote operations and substantial subsurface uncertainty to complete a set of high deliverability wells providing the majority of gas for LNG export. The high capacity of these wells enabled early ramp-up of the PNG LNG project, with continued strong performance enabling the LNG plant to operate significantly above nameplate capacity.
AAPG Datapages/Search and Discovery Article #90371 © 2020 AAPG Asia Pacific Region, The 1st AAPG/EAGE PNG Geosciences Conference, PNG’s Oil and Gas Industry: Maturing Through Exploration and Production, Port Moresby, Papua New Guinea, February 25-27, 2020