Experimental Evaluation Of The Mechanisms And Degree Of Fuzzy-ball Induced Damage In Single And Double-layer Tight Reservoirs

During different phases of Oilfield operations,the reservoir is highly prone to formation damage caused by fine migration or incompatible working fluids,which inevitably decreases the well’s performance.Several techniques for quantifying formation damage have been developed by deploying accessible data to obtain the type,range,and degree of damage.A recent study proposed the flow rate technique to complement the existing permeability index during the laboratory assessment of reservor damage caused by working fluid in single and multi-layer commingled tight reservoirs.However,the analysis performed in the study utilized simulated working fluids which could provide unrealistic conclusions.The fuzzy-ball working fluids(FBWFs)have been reportedly applied to several single-layer and multi-layer commingled tight reservoirs globally.Field reports have shown that FBWFs satisfactorily met all the operational and reservoir damage control requirements during their application in tight reservoirs.However,until now,there is no comprehensive experimental report on the degree of fuzzy-ball induced damage in single-and multi-layer tight reservoirs.Moreso,the formation damage-control mechanisms of the FBWF are yet to be studied.Therefore,there is an urgent need to investigate the damage degree and damage-control mechanisms of the FBWF thereby establishing an optimal field application technique that would guide the future application of FBWF in single and multi-layer tight reservoirs.This master’s thesis presents a detailed experimental study addressing the aforementioned research gaps and the core progress made is embodied herein as follows:1.Through microscopy observation and rheological testing,examines the microstructure and flow behavior of the FBWF under static and dynamic conditions,and the correspondence between the shear rates and shearing stresses of the FBWFs with varying densities under room and high temperature and pressure.This lays a foundation for further analysis by providing background information on the experimental design of FBWFs and their rheological stability under extreme operating conditions.2.Through single-and multi-layer core flooding experiments,estimate the degree of fuzzy-ball induced damage in single-and double-layer reservoirs via permeability and flow rate method,using core samples of different lithology from Linxing block.In addition,determine the permeability recovery rate after formation damage by FBWFs.The results show that:(a)For single-layer systems,the FBWF induced weak damage on coal seams and medium-to-weak damage on sandstones,and the results of the permeability and flow rate index were close with an error difference below 1%.The permeability recovery rate was above 66 %.(b)For doublelayer commingled systems,the overall degree of damage could not be evaluated by the permeability method.However,the flow rate index revealed weak damage,and thus,the overall damage in double-layer was lower than the single-layer reservoirs.These results verify the degree of fuzzy-ball induced damage and the feasibility of applying the flow rate index in single-and double-layer reservoirs.3.Through an SEM/EDS microscopic analysis,establish the mechanisms of fuzzy-ball induced damage in tight coal,carbonate,and sandstone core plugs from the Linxing block.The result indicates no significant alteration in the core structure with no evidence of fines migration.Additionally,the dissolution of Lead and Sulfur occurred in the coal seam,while Tellurium in sandstone,and Aluminum,Magnesium in carbonate.However,the precipitation of Aluminum,Magnesium,and Sodium occurred in sandstone with no precipitates found in coal and carbonate.The results present a reliable framework for analyzing the damage-control processes of FBWFs.4.The temporal plugging and dispersion characteristics of the FBWFs enable the generation of reservoir protection layers that minimizes formation damage due to solid and fluid invasion.However,the plugging rate was identified as a critical requirement.The damage control of the FBWFs is limited by the pH value which could lead to alkaline-sensitivity damage.5.The field implementation of the low-damaging FBWFs can be enhanced by optimizing the fluid additives,reservoir properties,and engineering parameters.In this regard,a workflow for optimal and strategic application of low-damaging FBWFs is proposed.The research work in this thesis provides a scientific basis for understanding the extent of fuzzyball induced damage in single-and multi-layer commingled tight reservoirs and serves as a guide for future design and strategic application of FBWFs in tight reservoirs.