Abstract
Optimal well placement seeks to achieve two seemingly contradictory objectives. For the short term, the well needs to establish the longest possible contact with the productive zone in order to enhance early production. For the long term production strategy of the field, the challenge is to maximize the total volume of hydrocarbon produced during the life of the field.
The first objective can be readily achieved by staying away from all reservoir boundaries at all times; this includes the oil-water contact and the cap rock for an oil reservoir. The second objective requires, depending on the situation, that the well be placed immediately below the cap rock, immediately above the oil-water contact, or at some predefined distance away. Precise well placement and proactive geosteering are required to achieve both objectives simultaneously.
A new azimuthal deep resistivity LWD device was recently evaluated and field tested in a field in Saudi Arabia. The stated objective of the run was to measure resistivity azimuthally and to assess the electrical anisotropy in the reservoir. In addition to anisotropy and resistivity determination, memory data was acquired in the process and later used to simulate situations in the field where real time geosteering decisions were required.
The up-down phase propagation logs gave a visual indication of the approaching boundaries, showing whether to expect it from below or above the well. The additional deep Geosignal measurement provided an early warning of the approaching boundaries long before the actual intersection was confirmed by borehole imaging. Multiple images at three depths of investigation showed progressively a bed of interest entering sequentially into the fields of investigation of the various measurements. Quantitative distance-to-bed boundary also helped derive the rate of approach of the boundary. Combined with images at different depths of investigation and with up-down resistivity, the information enabled informed real time decision-making for evasive action and proactive geosteering in future deployments.
