Robert L. Kleinberg

Nuclear magnetic resonance pulse sequences for use with borehole logging tools

An NMR pulse sequence for use in the borehole environment is provided which combines a modified fast inversion recovery (FIR) pulse sequence with a series of more than ten, and typically hundreds, of CPMG pulses according to [Wi -180-τi -90-(tcp -180-tcp -echo)j ]i where j is the index of the CPMG echoes gathered, i is the index of the wait times in the pulse sequence, Wi are the wait times, i are the recovery times before the CPMG pulses, and tcp is the Carr-Purcell spacing. Measurements are made of the signals induced in the formation as a result of the magnetic fields. Determinations of Mo and/or T1 are then made from the measurements according to relationships which relate Mpo, T1 and T2 to the signal magnitude. Other relationships which provide stretched exponentials or multiple exponentials can also be used. From the Mo and/or T1 determinations, formation parameters such as porosity and permeability may be derived according to equations known in the art. In obtaining the most accurate determinations of formation parameters in the least amount of time, the various pulse sequence parameters (I, J, Wi, and τi) are optimized prior to logging. Additional accuracy is obtained by integrating a gated portion of the echoes rather than by measuring amplitude, and by utilizing a phase alternated CPMG sequence in repetitive measurements in order to eliminate baseline shift error.

Borehole measurement of NMR characteristics of earth formations, and interpretations thereof

Borehole NMR logging apparatus and methods, and methods for the interpretation thereof. A logging tool is provided which produces a strong, static and homogeneous magnetic field B0 in a Volume of an adjacent formation on one side of the tool to measure nuclear magnetic resonance characteristics thereof. In the preferred embodiment, the tool has an RF antenna mounted on the outside of the metal body of the tool, directing focussed oscillating magnetic fields B1 at said Volume to polarize or tip the magnetic moments of hydrogen nuclei of fluids within rock pores. The same antenna can be used to receive signals of proton precession in the Volume of interest immediately after transmission of the RF polarizing field B1. Extremely rapid damping of the antenna between the transmitting and receiving modes of operation is accomplished by a Q-switch disclosed herein. The invention provides for the direct measurement of NMR decay having transverse relaxation time T2 behavior, and further provides for the fast repetition of pulsed measurements from within a borehole. An additional magnet array may be mounted offset from the first magnet configuration to prepolarize a formation before it is measured in order to pre-align a larger number of protons than the single magnet configuration could do by itself. Additional features of the invention are disclosed which increase the Signal/Noise ratio of the measured data, and improve the quality and quantity of borehole NMR measurements, per unit of time spent. Disclosed interpretation methods determine fluid flow permeability and longitudinal relaxation time T1 -type parameters by directly comparing the measured decay signals (such as T2 and T2 * type decay) to a representation which responds to both the decay time tdec and the imposed polarization period prior to such decay, tpol. The parameters of amplitude and T1 are determined and combined with certain preferred methods to generate robust values of formation characteristics such as fluid flow permeability. Other related methods are disclosed.

Noncontacting electrical conductivity sensor for remote, hostile environments

A device for measuring the electrical conductivity at the surface of a large or semi-infinite body at centimeter scale has been developed. The right frequency contacting measurement uses single turn transmitter and receiver loops to generate and detect eddy currents in the material to be probed. Response is linear in conductivity over the four decades of interest in geophysical investigations. The mechanical design of the sensor makes it insensitive to temperature and pressure changes, and to accelerations, impact, and abrasion. Therefore, it is operable in remote, hostile environments such as deep boreholes. >

Microinduction Sensor for the Oil-Based Mud Dipmeter

Microinduction sensors are used in the Oil-Based Mud Dipmeter Tool to measure formation conductivity through nonconductive mud or mudcake. The sensor consists of small transmitter and receiver coils mounted in a pad. An extensive research effort involving sensor response modeling, laboratory experiments, and signal processing contributed to the development of these new sensors.

A Multi-Measurement Core-Log Integration for Advanced Formation Evaluation of Source Rock Formations: A Green River Case study

Historically, well logging and interpretation workflows have been developed mainly for use in porous and permeable reservoir formations and are not commonly used to evaluate source rocks or unconventional reservoirs. Instead, the evaluation of source rocks, such as the organic-rich deposits of the Green River Formation, has relied primarily on expensive and inefficient core analyses such as the Fischer Assay and simple log interpretation. With the potential oil equivalent in place exceeding a trillion barrels, there is a need for detailed characterization of these oil shale deposits using high resolution well logs. We have logged two Green River wells using combinations of standard and advanced logging techniques. This program was supported by extensive core analysis, including Fischer assay and thorough mineralogical and chemical analyses. Methods of determining kerogen content from log responses were developed along with multiple methods of estimating a continuous log of formation water salinity. We developed methods for quantitatively evaluating these Green River oil shales by integrating standard logs with more advanced logging measurements including nuclear magnetic resonance, elemental capture and inelastic spectroscopy, and dielectric dispersion. The results and the petrophysically derived multi-mineral model are validated by the core measurements and then applied to a near-by well.

Theory Of Microinduction Measurements

U.S.A. Abs tract The microinduction sensor consists of miniature transmitter and re- ceiver coils. It can be used to make a non-contacting conductivity mea- surement of inhomogeneous media. Due to the small siee of the sensor, it is capable of centimeter resolution, and is therefore useful in geophysics probing, nondestructive testing and metal detector. The theory of the microinduction sensor is described. Keywords: geophysics probing, induction, microinduction, theory, metal detector.