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Abstract
The selection of a drill bit is an essential issue in well planning. Furthermore, identification and evaluation of sedimentary rocks before well drilling plays a crucial role in choosing the drill bit. Moreover, the Markov chain as a stochastic model is one of the powerful methods for identifying lithological units, which is based on the calculation of the transition probability matrix or transition matrix. The Markov chain experiences transitions from one state (a situation or set of values) to another according to specified probabilistic rules. In this paper, the Markov chain was implemented for bit selection in a formation with different sedimentary facies (such as the Dashtak Formation). Therefore, the proper drill bit was proposed by utilizing the transition matrix of rock facies and the available bits. This process was carried out in two wells where the thicknesses of the Dashtak Formation are 960 meters and 1410 meters. Consequently, the results indicate that the Markov chain is a practical method for selecting bits in a sequence of rock facies based on an acceptable matching between the reality mode (the used bits in the well) and the Markov chain results. Besides, in the case of using an improper bit in a well, and using a bit in a washing and reaming operation, there were differences between the used bits and the Markov chain outputs.
Highlights
Drilling oil and gas wells has encountered various challenges from the beginning
The purpose of this study is to utilize a probabilistic method to select a suitable drill bit in this formation, given that the Markov chain has been introduced as a powerful method for modelling rock facies
According to this Figure, six steps were defined to go through this algorithm, which are as follows: Step 1: The state space was determined, according to the variable under study and as a result, state space is equal to the number of existing facies in any sedimentary sequence (Nikoogoftar et al, 2013)
Summary
Drilling oil and gas wells has encountered various challenges from the beginning. New technologies are being discovered to solve critical technical problems in smart and cost-effective ways. The purpose of this study is to utilize a probabilistic method to select a suitable drill bit in this formation, given that the Markov chain has been introduced as a powerful method for modelling rock facies. The present study, the application of the Markov chain probabilistic method in simulating rock facies and selecting a drill bit in one of the Iranian formations was proposed. Due to the presence of thick anhydrite layers, this formation is considered as an important cap rock in the Zagros Basin for gas reservoirs of the Dahrom Group (Dalan and Kangan) in the south of Iran (Khoshnoodkia et al, 2010; HajianBarzi et al, 2015; Rahmani et al, 2018; Habibnia et al, 2016).
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