The data delivered by a new reservoir mapping while drilling (RMWD) tool provides more geological information than that from any other logging-while-drilling (LWD) technology previously available in the oil field. Its answer product images the surrounding formation structure, and the resulting maps can be used by the geoscientists to improve their understanding of the subsurface, the well placement and the reservoir.To take advantage of the richness of the measurements and deep depth of investigation across multiple formation boundaries, an automatic stochastic inversion has been developed that combines approximately a hundred phase and attenuation measurements at various frequencies and transmitter-to-receiver distances. This efficient Bayesian model-based stochastic inversion runs in parallel with multiple independent search instances that randomly sample hundreds of thousands of formation models using a Markov chain Monte Carlo method. All samples above a quality threshold over the solution space are used to generate the distribution of formation models that intrinsically contain the information for model uncertainties.RMWD is a highly nonlinear problem; inverting for a unique solution is analytically difficult due to the well-known local minima issue. The stochastic method addresses that by sampling thousands of possible formation models and outputting a distribution of layered models that are consistent with the measurements. Statistical distributions are displayed for formation resistivity, anisotropy and dip at each logging point. Additionally, the median formation models for resistivity are shown along the well trajectory as a curtain section plot. This provides an intuitive interpretation for the entire reservoir formation around the tool. The inversion curtain section plot can be overlaid with the seismic formation model for combined interpretation. Furthermore, the curtain plot provides graphical information for dip and distance to boundary, which are critical for field applications such as landing, geosteering, remote fluid contact identification, etc. The stochastic-sampling-based answer product has been intensively field tested and has proven to provide reliable estimation of the formation geometries and fluid distributions in many locations and geological environments worldwide.Field applications and simulated examples of the stochastic inversion include remote detection of the reservoir to enable accurate landing, navigating multilayered reservoirs, remote identification of fluid contacts and reservoir characterization in the presence of faults. The stochastic inversion samples the formation properties randomly and provides the distribution of formation properties based on a large number of samples, instead of providing only the most likely solution as is typical for deterministic inversions. A statistical method of presenting inversion results in formation space provides an instant and intuitive understanding of the formation surrounding the tool. Quantifying the non-uniqueness of the inverted fo...
An experimental pulsed-neutron logging-while-drilling (LWD) tool is currently under field test. The tool provides a suite of nuclear measurements that include neutron porosity, thermal neutron capture cross section (i.e. sigma), pulsed-neutron density and the relative abundance of certain elements (e.g., calcium, silicon, iron, sulfur, etc.) that are used to calculate mineralogy. The tool provides azimuthal measurements in real time that are useful for geosteering applications. Use of a pulsed-neutron source eliminates the need for radioactive-chemical sources that are used in conventional nuclear LWD tools. This results in increased wellsite safety and efficiency. Procedures and equipment required for radioactive-source handling, storage and retrieval are also eliminated. The experimental LWD tool is the result of a joint collaboration that began in 1995 between the Japan National Oil Corporation and Schlumberger. The primary goal of the tool is to demonstrate feasibility of pulsed-neutron measurements in the hostile LWD environment. Introduction An experimental pulsed-neutron LWD tool has been developed that has successfully logged several test wells. The prototype tool represents a merging of pulsed-neutron wireline measurements with LWD measurement technology. The applications of pulsed-neutron measurements for formation evaluation are well established. Pulsed-neutron wireline tools are used to determine water saturation, neutron porosity and formation mineralogy in both open and cased holes. In addition to the rich variety of measurements, pulsed-neutron technology eliminates the radioactive-chemical sources used in conventional nuclear tools. Source-storage pits, transport shields, loading shields, collar shields and handling tools are therefore not required. Transportation logistics, wellsite safety and wellsite efficiency are all improved.
A new pulsed nuclear magnetic resonance (NMR) logging tool, known as the CMR* Combinable Magnetic Resonance tool, is being used worldwide. During the CMR tool development phase, one challenge was to design a robust and economical data acquisition and signal processing scheme for the hundreds or thousands of spin- echo amplitudes that can be acquired during the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. This challenge was met by developing a new signal processing and associated downhole data compression algorithm. Data compression is essential to reducing the processing times so that formation T2-distributions can be estimated in real time. Compression of the digital data is possible, without loss of information, because the linear dependency of the NMR measurement kernels results in gross redundancy of the measured spin-echo amplitudes. An attractive feature of the algorithm described in this paper is that the compression can be performed in the downhole tool, thus substantially reducing the telemetry requirements. The raw spin echoes can also be sent uphole and made available for additional processing. Logs of CMR porosity, free-fluid porosity, mean relaxation time and rock permeability are computed from the estimated T2-distributions. The accuracy and precision of the CMR log Outputs are demonstrated by repetitive Monte Carlo computer simulations in which noisy, synthetic spin-echo amplitudes are generated from known T2-distributions and then processed to obtain log outputs. Monte Carlo simulations are used to elucidate CMR log responses in typical clean sand, shaly sand, and carbonate rocks. The relative insensitivity of the measurements to short relaxation times (e.g., those less than a few milliseconds) is discussed and used to explain the differences between CMR log porosity and "total" formation porosity in shaly formations. We show that CMR porosity is an "effective porosity" that does not include clay bound water and microporosity having relaxation times less than a few milliseconds. We give examples of statistical fluctuations that can occur on estimated T2-distributions to assist log analysts in recognizing artifacts that are not indicative of actual reservoir rock properties. Field logs that display many of the features of CMR log responses revealed by the simulations are also presented. Introduction The physics underlying pulsed NMR has been known since 1950. Pulsed NMR has been used since its discovery as a probe for studying the macroscopic and microscopic properties of condensed matter. Its original applications were in industrial and academic laboratories. More recently, magnetic resonance imaging has become a powerful nonradioactive diagnostic tool for medical research and clinical applications. The recent development of pulsed NMR well logging tools had to await the development of new technology, e.g., integrated circuits, microprocessors, and stable high-field permanent magnets. The CMR tool is a product of these technological advances and years of research4 and development effort. The CMR tool is a pad-type tool that performs pulsed NMR measurements using Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. The spin-echo signals acquired during the measurement are derived from protons (i.e., hydrogen nuclei) that precess in the static magnetic field produced by a permanent magnet in the sonde. The protons are contained in the fluids that occupy the rock pore spaces. A CPMG consists of two time intervals:an initial wait time during which the proton magnetization approaches its thermal equilibrium value in the static magnetic field andthe echo collection period during which a set of radio frequency (RF) pulses generated by an antenna in the sonde are used to generate the spin echoes. The nominal tool inter-echo spacing is 0.32 ms. The wait time interval normally accounts for most of the CPMG measurement time. P. 301
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.