We invite you to SPE young professionals meeting on "A method for diagnostics of near-wellbore zone properties alteration by combination of hydrodynamic and geophysical modeling". by Anastasiya Makarova, Consultant, Schlumberger Moscow Research.
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Meeting will take place on 26 May, Thursday, at 19-00 hours at Sushchevskiy val, 2, Moscow.
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More details about the topic
During drilling and completion operations, mud filtrate and different mud components (particles, clay, polymers etc.) do invade into the near-wellbore zone of the reservoir due to the ‘over-balance’ pressure and create multizone structures: we identify an external mudcake (mud-solid components deposited at the sandface), an internal mudcake (formed by mud components invaded into the reservoir formation), and several mud-filtrate-invaded zones. The invaded mud filtrate can interact with the minerals of the formation and modify its properties.
As a result, these processes can lead to higher values of skin factor. The electrical resistivity also significantly changes due to the different electrical conductivities of mud filtrate, formation water and oil. It well known that it strongly impacts the resistivity log data. Well logging is traditionally focused on the investigation of the formation properties in the noninvaded (“virgin”) formation. The invaded zone is considered by some as a “nuisance object”, but contains important information indicative of mobility and saturation.
The mathematical modeling of the direct resistivity log is considered, taking into account the transient alteration of reservoir properties and fluid saturations in the near-wellbore zone due to invasion/removal components of drilling mud (or other technological fluids).
The distribution of the electrical resistivity of each layer is simulated on the basis of results of hydrodynamic modelling of mud invasion process with taking into account salt transport and salt exchange between mud filtrate and reservoir water. For validation purpose, the simulated results were compared with analytical solution for simple homogeneous axisymmetric problem and with some log charts including the influence of the wellbore, the invaded zone and the finite thickness of the formation layers. The conventional log charts are obtained under assumption of step-function distribution of mud filtrate and don’t take into account the complex specific of transient hydrodynamic processes in the near-wellbore zone.
The modification of the near-wellbore zone properties is considered due to mud filtrate invasion, fines migration, wettability alteration (as a result of interaction between invaded mud surfactant, polymer and etc. and pore walls), capillary imbibition, and the impact of these processes on the characteristics of damaging, well cleanup, production and on resistivity log data.
Transient in nature, this new model shows that conventional log charts for typical mud losses could be in error of apparent resistivity as much as 50% due to capillary imbibition, fines migration and relative permeability alteration, because the log chats don’t consider the full complexity of near-wellbore invasion and cleanup processes.
The developed technique includes a mathematical model of the transient behavior of near-wellbore multiphase phenomena which takes into account the mud component invasion/removal. It simulates the log response of the resistivity. It allows for the diagnosis, the evaluation, the prevention, the remediation, and the control of the alteration of near-wellbore properties.
The investigation is carried out for synthetic and literature field cases to confirm the efficiency of the developed method for assessing of NWZ damage.
About author
Anastasiya Makarova, Consultant, Schlumberger Moscow Research.
Anastasiya graduated as MSc in engineering and technology from department “Oil and Gas Field Development” of Gubkin Russian State University of oil and gas in 2012. PhD degree was conferred in 2015. Anastasiya has been working in Schlumberger Moscow Research since 2010. She is a SPE member since 2014.