Abstract

Dipmeter & image logging tools had gained wide acceptance in petroleum industry as a mean to define subsurface sedimentary structures and to detect geologic signatures of tectonic events. The advantage of dipmeter & image logging, over seismic is that they rely on their ability to provides accurate information's near the well bore and detect structural features beyond seismic resolution.

Dipmeter & Imaging information in frontier areas with poor seismic imaging (scattered 2D seismic data over thrust & belt regime) is paramount from wildcat spud, mainly to initially correlate with surface geological data, later on constantly update the geological model and, of course, to visualize expected geological prognosis for the undrilled section. In the Kurdistan region (Iraq) usually the surface sections are drilled with air/foam air due to existing drilling risks. An operational imposed mud system that triggers several limitation from the data acquisition point of view. In this case the Joint Venture (Repsol Exploration as an Operator and Maersk as a partner) decided to use a High Definition Formation Micro Imager as a challenge against the lack of other wireline logging reliable tools (Sonic, etc…). Initially this High Definition Formation Micro Imager with its high vertical resolution of 0.2”, was designed electronically for greater reliability and clearer images in extreme conditions, could provide an excellent image in Air/Foam mud. This tool data revealed that the dip patterns over the intervals suffer from increasing and decreasing of dips downward with repeated azimuth directions (generally from NE to SW). These changes were not accompanied by any fracture displacement (faulting). These zones were interpreted due to the presence of series of recumbent and overturned folding, where the direction of dip decreases till the axial plane of the structure, then increasing again towards the opposite flank with different azimuth direction. This interpretation helped matching the updated geological model (unexpected recumbent & overturned folding) with the surface geology, and determined a startup (geological prognosis) for the undrilled section.

This paper documents that a High Definition Formation Micro Imager can be successfully acquired in such tough Air/Foam mud conditions. It also provided reliable downhole information for surface section project decision. This data proved to be very important to update the geological model and provide a required geological prognosis.

You can access this article if you purchase or spend a download.