Andrew C Morton¹
(1) British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom

Abstract: Geosteering of high-angle wells using Heavy Mineral Analysis

The geosteering toolkit (LWD, cuttings evaluation and biostratigraphy) frequently lacks a vital component during drilling non-marine clastic reservoirs. Such sequences generally lack a high-resolution biostratigraphic framework for reservoir correlation. By contrast, since detrital heavy minerals are ubiquitous in such sequences, heavy mineral analysis (HMA) is a potential replacement for the biostratigraphic component.

This paper presents the results of a feasibility study into the use of HMA as a tool for geosteering in Paleozoic fluvial-aeolian reservoirs of NW Europe. The study concentrated on a reservoir sequence comprising an upper fluvial unit (poor quality), a middle aeolian unit (good quality), and a lower mixed fluvial-aeolian unit (moderate quality). Consequently, high-angle drilling would target the middle unit, with the upper unit to be avoided as far as possible. Drilling of the lower unit could be tolerated, but would be best avoided.

Prior to its application at wellsite, it was necessary to show that the method provides adequate, repeatable distinction between the three units. Study of core material from an offset well identified a major event at the boundary between the middle and upper units, and another within the upper part of the lower unit. Further work established that these events were laterally extensive, and were identifiable using cuttings material. Following the positive outcome of the feasibility study, it was considered that HMA provided sufficient resolution for the method to be used to monitor two high-angle wells. The stratigraphic implications of the HMA data will be illustrated by reference to these two wells.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana