Impact of Conveyance System on Reservoir Characterization: New Opportunity for Highly Deviated Wells

Abstract

The recent trend toward drilling horizontal wells with complicated geometries in complex reservoirs has led to operational challenges. While LWD logs are often well suited in these environments, circumstances such as very small wellbores, tool availability, and high costs sometimes lead to a search for alternative means of acquiring a full suite of formation evaluation data. The objective of this paper is to show how, in a very complex reservoir, the choice of conveyance system can be strategic, particularly in the context of data quality and risk mitigation. The conveyance system considered is comprised of wireline tools which are housed inside drill pipe. When the borehole assembly reaches the toe of the lateral, a dart is pumped down, which releases the formation evaluation assembly and turns on the data acquisition. As the pipe is tripped out of the hole, the tools acquire data in memory. The presented case study considers a field in Southern Europe where a fractured carbonate reservoir is developed with horizontal wells. Characteristics of the reservoir are very high resistivity, wellbore stability issues, presence of asphaltenes, and 6″ bit sizes. To fully characterize the reservoir properties and understand the natural fracture networks, electrical imaging, gamma-ray, dipole sonic and caliper data were acquired. The integration of the dipole sonic and electric image logs provided the basic information to perform the matrix and the fractures evaluation as well as the anisotropy orientation and the best fluid path characterization. The availability of mechanical caliper led the decrease of the uncertainty in the interpretation and the optimization of the lower completion placement. A comparison between LWD and WL image logs is presented to rate the real added value of the wireline acquisition. This new approach using an alternative conveyance system enabled proper reservoir characterization. In addition to the high quality of the results there was also a reduced exposure to potential risks including stuck and lost in hole tools. The general pros and cons as well as cost considerations are discussed. While the conveyance system is generally considered a drilling focused solution and is therefore most influenced by operational challenges, it should also be considered an additional resource for the petrophysicist and geologist performing essential data interpretation as proven by the presented case study.