The sensitivity of the array resistivity log to mud filtrate invasion and its primary five-parameter inversion for improved oil water recognition

In order to improve reservoir fluid recognition, the sensitivity of array resistivity response to the difference of the invasion properties in both oil-bearing layers and water layers is analyzed. Then the primary inversion is carried out based on the array resistivity log. The mud invasion process is numerically simulated based on the oil-water flow equation and water convection diffusion equation. The results show that the radial resistivity of a fresh mud-invaded oil-bearing layer presents complex distribution characteristics, such as nonlinear increase, increasing to decreasing and low resistivity annulus, and the resistive invasion profile of a water layer is monotonic. Under specific conditions, array resistivity log can reflect these changes and the array induction log is more sensitive. Nevertheless, due to the effect of factors like large invasion depth, reservoir physical and oil-bearing properties, the measured apparent resistivity may differ greatly from the actual mud filtrate invasion profile in an oil-bearing layer. We proposed a five-parameter formation model to simulate the complex resistivity distribution of fresh mud-invaded formation. Then, based on the principle of non-linear least squares, the measured array resistivity log is used for inversion with the Marquardt method. It is demonstrated that the inverted resistivity is typically non-monotonic in oil-bearing layers and is monotonic in water layers. Processing of some field data shows that this is helpful in achieving efficient reservoir fluid recognition.

Fast anisotropic resistivities inversion of loggingwhile-drilling resistivity measurements in highangle and horizontal wells

Information about anisotropic resistivity is essential in real-time correlation,updating of formation model and making more confi dent geosteering decisions in logging-while-drilling(LWD)application.However,abnormal responses such as curve separations and apparent resistivity“horns”often exist in the LWD resistivity measurements due to the infl uences of complex downhole environments.Thus,accurate formation resistivity is not readily available.In this paper,we present an effi cient inversion scheme for the rapid estimation of anisotropic resistivity from LWD resistivity measurements acquired in high-angle and horizontal wells.Several strategies are adopted in the inversion:(1)a one-dimensional(1D)simulator with a simplifi ed three-layered model guarantees the forward speed and keeps the number of inverted parameters as few as possible;(2)combined with geological and petrophysical bounds,the tool constraints derived from a detection capability analysis of LWD resistivity measurements are applied to scale down the inverted parameters’searching scope,which avoids meaningless solutions and accelerates the inversion signifi cantly;(3)multiple-initial guesses are used in the inversion to ensure a global solution.Inversion results over synthetic examples demonstrate that the proposed 1D inversion algorithm is well suited for complex formation structures.It is also robust and fast in extracting anisotropic resistivities from LWD resistivity measurements.

Resistivity Logs of the Chinese Continental Scientific Drilling Main Hole:Implication for the Crustal Electrical Structure of Dabie-Sulu Terrane,Central-Eastern China

To understand the electrical structure of the Sulu（苏鲁） terrane,we analyzed the resis-tivity logs of the Chinese Continental Scientific Drilling main hole（CCSD-MH） and obtained the statis-tical characteristics of the resistivity log of ultrahigh-pressure（UHP） metamorphic rocks.To check the logs＇ quality,we compared the resistivity log data with the core test data.The two datasets show a good coherence.On the whole,the resistivity of the UHP metamorphic rocks from the CCSD-MH is very high（mostly higher than 1 000 ？？m）.From orthogneiss to paragneiss,amphibolite,retrograded eclogite,rutile eclogite,phengite eclogite,and ultramafic rock,the resistivity decreases gradually.The fracture zone,enrichment of metal minerals,and serpentinization of peridotite can probably cause the decrease of resistivity.Comparing the electrical structure of the crust of Dabie（大别） terrane and Sulu terrane,we can conclude that（1） the electrical structure of the crust of Dabie terrane and Sulu terrane shows a very big difference,（2） the high-resistivity zone of the north Sulu orogen extended to a very great depth（60 km）,but the high-resistivity zone of Dabie orogen is over the depth of 25 km.

Deep resistivity "turnover" effect at oil generation "peak" in the Woodford Shale,Anadarko Basin,USA

The Devonian Woodford Shale in the Anadarko Basin is a highly organic,hydrocarbon source rock.Accurate values of vitrinite reflectance(R_o)present in the Woodford Shale penetrated by 52 control wells were measured directly.These vitrinite reflectance values,when plotted against borehole resistivity for the middle member of the Woodford Shale in the wells,display a rarely reported finding that deep resistivity readings decrease as R_o increases when R_o is greater than 0.90%.This phenomenon may be attributed to that aromatic and resin compounds containing conjugated pi bonds generated within source rocks are more electrically conductive than aliphatic compounds.And aromatic and resin fractions were generated more than aliphatic fraction when source rock maturity further increases beyond oil peak.The finding of the relationship between deep resistivity and R_o may re-investigate the previously found linear relationship between source rock formation and aid to unconventional play exploration.