Application of High-Resolution Core Thermal Profiling to Optimize Well Construction Process for Unconventional Reservoir
Authors: Tatur Olga , Popov Evgeny , Popov Yuriy , Stukachev Vladimir , Chekhonin Evgeny , Cheremisin Alexey , Petrakov Yuriy , Sobolev Alexey , Cheremisin Alexandr 
Published: October 2018

Geomechanical modeling and wellbore stability calculation it's like "new standard" at present time for drilling optimization of production and exploration wells. Geomechanical modelling take into account stress state, elastic and strength rock properties allows to calculate range of drilling mud density for safety drilling (for exclude breakouts, losses, HF while drilling).

Input data for construction such models are continuous profiles of the distribution of static mechanical properties of the rock, which are built based direct measurements from core data and using logs results (acoustic, density logs, correlations of Logs-Core). Direct measurements from core data always have best accuracy and reliable. But such measurements are very discrete and limited for economic and technological reasons. Thus, during of construction a model of mechanical properties, the main problem aria is a correct distribution of properties along the trajectory of a future well if we have just discrete limited direct measurements of the geomechanical properties from the core. For the correct decision is necessary: Correctly identify places for core sample for research to identified mechanical types of rock for maximum coverage of all facies.Identify different mechanical facies in a lithological heterogeneous section when we have limited logs data for one or another reasons (complex lithology, bad log quality).

For the identification of mechanical facies often uses the scratch test method. The method that allows by scratching a full-length core with a special tool, recalculate the measured load parameters into a continuous profile of geomechanical properties (UCS – unconfined compressive strength) [5]. There are some limitations for use this method – it's possibility of damaging the full-size core under mechanical impact, the need to transport the full-size core to special laboratories, the high cost of research, mandatory core damage (groove from the measuring head, especially when we work with unconsolidated rocks).

An alternative to scratching is the technology of continuous high-resolution thermophysical core profiling. The technology is based on the method of optical scanning recommended by the International Association of Geomechanics (ISRM) [6]. In low-permeability, organic-rich sedimentary deposits, the thermal properties has well correlation with the mechanical properties of core. It was confirmed by a lot of laboratory tests and pilot industrial works [3, 4].

During the construction wellbore stability model for a horizontal well of one of the fields in Western Siberia, the authors performed high-resolution continuous thermophysical profiling of a full-size from Bazhenov and Abalak formation. Correlation between logs and core data were constructed, the details of the sonic log data and the prediction of acoustic characteristics in the intervals with poor-quality sonic log data were performed.

The integrated analysis of log data and continuous thermophysical profiling data on the core enabled to: Identify the mechanical facies in the formation and select the optimal place for a limited number of core samples from different mechanical facies for a full description of the elastic-strength properties of the formation based on the core test results.Make depth matching between core data and logs data.Build correlation "Thermal Properties-Logs-Core" for elastic strength properties based on direct measurements on the core material.Create a continuous model of mechanical properties along the well trajectory.

Geomechanical modeling for the sediments of the Bazheno-Abalak complex (BAC) made it possible to successfully drill the first horizontal wells in the field. The drilling results showed a good convergence of the stability model with the actual state of the well.