Electricity: measuring and testing – Particle precession resonance – Using well logging device
Reexamination Certificate
2000-08-10
2003-12-09
Gutierrez, Diego (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using well logging device
Reexamination Certificate
active
06661226
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to borehole measurements and more particularly to a system and method for detecting the presence and estimating the quantity of gaseous and liquid hydrocarbons using nuclear magnetic resonance.
BACKGROUND
Various methods exist for performing measurements of petrophysical parameters in a geologic formation. Nuclear magnetic resonance (NMR) logging, which is the focus of this invention, is among the best methods that have been developed for a rapid determination of such parameters, which include formation porosity, composition of the formation fluid, the quantity of movable fluid and permeability, among others. NMR measurements are environmentally safe and are essentially unaffected by matrix mineralogy, because NMR signals from the matrix decay too quickly to be detected by the current generation NMR logging tools. Thus, unlike conventional neutron, density, sonic, and resistivity logs, NMR logs provide information only on formation fluids. Importantly, however, NMR tools are capable of directly measuring rock porosity filled with the fluids. Even more important is the unique capability of NMR tools, such as NUMAR Corporation's MRIL® tool to distinguish among different fluid types, in particular, clay-bound water, capillary-bound water, movable water, gas, light oil, medium oil, and heavy oil by applying different sets of user-adjusted measurement parameters. (MRIL is a mark of NUMAR Corporation, a Halliburton company). This ability to detect the presence and estimate the volumes of different types of fluids is becoming one of the main concerns in the examination of the petrophysical properties of a geologic formation.
To better appreciate how NMR logging can be used for fluid signal separation and estimating fluid volumes, it is helpful to briefly examine the type of parameters that can be measured using NMR techniques. It is well known that when an assembly of magnetic moments, such as those of hydrogen nuclei, are exposed in a NMR measurement to a static magnetic field they tend to align along the direction of the magnetic field, resulting in bulk magnetization. The rate at which equilibrium is established in such bulk magnetization upon provision of a static magnetic field is characterized by the parameter T
1
, known as the spin-lattice relaxation time. Another related and frequently used NMR logging parameter is the spin-spin relaxation time T
2
(also known as transverse relaxation time), which relaxation is the loss of transverse magnetization due to non-homogeneities varying in time in the local magnetic field over the sensing volume of the logging tool. Both relaxation times provide information about the formation porosity, the composition and quantity of the formation fluid, and others.
Another measurement parameter obtained in NMR logging is the diffusion of fluids in the formation. Generally, diffusion refers to the motion of atoms in a gaseous or liquid state due to their thermal energy. Self-diffusion is inversely related to the viscosity of the fluid, which is a parameter of considerable importance in borehole surveys. In a uniform magnetic field, diffusion has little effect on the decay rate of the measured NMR echoes. In a gradient magnetic field, however, diffusion causes atoms to move from their original positions to new ones, which moves also cause these atoms to acquire different phase shifts compared to atoms that did not move. This effect contributes to a faster rate of relaxation in a gradient magnetic field.
NMR measurements of these and other parameters of the geologic formation can be done using, for example, the centralized MRIL® tool made by NUMAR Corporation, a Halliburton company, and the sidewall CMR tool made by Schlumberger. The MRIL® tool is described, for example, in U.S. Pat. No. 4,710,713 to Taicher et al. and in various other publications including: “Spin Echo Magnetic Resonance Logging: Porosity and Free Fluid Index Determination,” by Miller, Paltiel, Gillen, Granot and Bouton, SPE 20561, 65th Annual Technical Conference of the SPE, New Orleans, La., Sep. 23-26, 1990; “Improved Log Quality With a Dual-Frequency Pulsed NMR Tool,” by Chandler, Drack, Miller and Prammer, SPE 28365, 69th Annual Technical Conference of the SPE, New Orleans, La., Sep. 25-28, 1994. Certain details of the structure and the use of the MRIL® tool, as well as the interpretation of various measurement parameters are also discussed in U.S. Pat. Nos. 4,717,876; 4,717,877; 4,717,878; 5,212,447; 5,280,243; 5,309,098; 5,412,320; 5,517,115, 5,557,200; 5,696,448 and 5,936,405, all of which are commonly owned by the assignee of the present invention. The Schlumberger CMR tool is described, for example, in U.S. Pat. Nos. 5,055,787 and 5,055,788 to Kleinberg et al. and further in “Novel NMR Apparatus for Investigating an External Sample,” by Kleinberg, Sezginer and Griffin, J. Magn. Reson. 97, 466-485, 1992. The content of the above patents and publications is hereby expressly incorporated by reference.
It has been observed that the mechanisms determining the measured values of T
1
, T
2
and diffusion depend on the molecular dynamics of the formation fluids being tested and on the types of fluids present. Thus, in bulk volume liquids, which typically are found in large pores of the formation, molecular dynamics is a function of both molecular size and inter-molecular interactions, which are different for each fluid. Water, gas and different types of oil each have different T
1
, T
2
and diffusivity values. On the other hand, molecular dynamics in a heterogeneous media, such as a porous solid that contains liquid in its pores, differs significantly from the dynamics of the bulk liquid, and generally depends on the mechanism of interaction between the liquid and the pores of the solid media. It will thus be appreciated that a correct interpretation of the measured signals can provide valuable information relating to the types of fluids involved, the structure of the formation and other well-logging parameters of interest.
If the only fluid in the formation is brine, a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence with a short inter-echo spacing (T
e
) and a long wait-time (T
w
) can be applied for porosity determination and identification of capillary-bound and free water volumes. Total porosity logging methods are available to improve the quality of data used for determining pore volumes occupied by clay-bound and/or capillary-bound water. (See, for example, Prammer, M. G., et al.: “Measurements of Clay-Bound Water and Total Porosity by Magnetic Resonance Logging,” paper SPE 36522 presented at the 1996 SPE Annual Technical Conference and Exhibition, Denver, October 6-9). However, if hydrocarbons, such as formation oil and/or gas or filtrate from oil-based mud, coexist with brine, porosity determination and fluid typing (identification and quantification) with NMR becomes more difficult.
Additional difficulties arise from the fact that NMR measurements impose limitations on the logging speed. For example, it is known in the art that for porosity determination all stimulated fluid protons should be sampled at full polarization. Therefore, a long wait time T
w
is required to completely detect the magnetization from protons in slow T
1
processes. For gas and light oil under typical formation conditions of temperature and pressure (100-300° F. and 2,000-10,000 psi), T
1
values of a few seconds occur at low-frequency (1- to 2-MHz) NMR. Wait times T
w
of at least 10 seconds will capture nearly all the total proton magnetization arising from the individual T
1
recovery rates encountered in petroleum logging. Such long wait times, combined with acceptable depth sampling, restrict the logging speed and reduce wellsite efficiency. One approach addressing this problem is the application of prepolarization and multislice (multifrequency) acquisitions implemented in the Magnetic Resonance Imaging Logging™ MRIL-Prime tool. See Prammer, M. G., et al.: “Theory and Operation of a New Multi-Volume NMR Logging System,” paper DD p
Aadireddy Prabhakar
Bouton, Jr. John C.
Coates George Richard
Galford James Elmer
Hou Lei Bob
Gutierrez Diego
Halliburton Energy Service,s Inc.
Pennie & Edmonds LLP
Vargas Dixomara
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