NEW RESISTIVITY MODELS FOR RESERVOIR MONITORING APPLICATIONS

摘要

Reserve recovery and resource progression is theprimary driver for economic and operationaldecisions pertaining to field development andproduction. In many fields, waterflood operationsare crucial to increasing hydrocarbon recovery. Ifproblems are encountered because of waterflood,they can cause excessive water handling, whichcan incur extra costs and result in bypassedreserves. To this end, any method of monitoringwater saturation in a formation is extremelyvaluable for managing production. Wirelinelogging tools have been used routinely to measureformation resistivity and have provided a reliablemethod to monitor waterfront at some distancefrom the wellbore in openhole or speciallycompleted monitoring wells. This paper will focuson another option—waterflood monitoringsystems that are permanently deployed behindcasing. These installations include sensors thatenable detection of approaching waterflood. Somework also has been performed on permanentinstallations within completion equipment to allowpermanent reservoir monitoring.Many solutions are available for addressingwaterflood that consider oil-/gas-field sizes,locations, and economics. However, depending oncost versus the anticipated field economics, apermanently installed continuous (time-lapse)waterflood monitoring system might offer themost viable solution, if the possible benefits canjustify the cost. The value of the system will alsobe enhanced by other reservoir monitoringrequirements, such as pressure, temperature, andother distributed measurements; therefore,combining a waterflood monitoring solution with amultizone, intelligent completion could helpprovide significant value, especially in sand-screenwells. Additionally, offshore installations,especially intelligent completions, offer a highvaluemarket for water monitoring systems.A permanent reservoir sensing system forwaterflood monitoring consists of an array ofelectromagnetic transmitters and receivers withvarious configurations. Accurate resistivity modelsof the reservoir are essential for job planning andsystem optimization, operation, and interpretation.However, some existing resistivity modelsoversimplify waterflood as a step transitionbetween oil- and water-saturated zones. Inaddition, most models assume that piston-shapedflooding will occur throughout the producing-zonethickness. These simplifications do not necessarilyhold in actual reservoirs and, therefore, feasibilitystudies based on such models can be highlyinaccurate.In this paper, realistic three-dimensional (3D)resistivity models based on dynamic reservoirsimulations of typical waterflood environments arebuilt. These models are developed to addressuncertainties, such as the “thickness” of thewaterflood front as it transitions from initial oil-inplace(OIP) to residual oil, the shape of thewaterflood front, and the residual oil saturationafter water flooding. Using the constructedmodels, a comparative study of electromagneticinduction and galvanic permanent monitoringsystems that operate within an appropriate powerstandard for offshore wells is conducted. Thesensitivity of each monitoring system to differentgeological features captured by the constructedresistivity models is compared. These featuresinclude geological uncertainty, laminatedformation (anisotropy), and waterflood fingeringin vertical and horizontal wells. This paper helpsclarify the situations in which a permanentlyinstalled continuous (time-lapse) waterfloodmonitoring system can provide significanteconomic advantages.