WO2009088501A1

WO2009088501A1 - System and method for memory pulsed-neutron gamma-ray spectroscopy logging

Info

Publication number: WO2009088501A1
Application number: PCT/US2008/050335
Authority: WO
Inventors: Daniel F. Dorffer; Clive Menezes; Donald L. Crawford
Original assignee: Truax, Jerome, A.; Halliburton Energy Services, Inc.
Priority date: 2008-01-05
Filing date: 2008-01-05
Publication date: 2009-07-16

Abstract

We disclose a modular battery-powered downhole logging tool, which may be a modular memory pulsed-neutron gamma ray spectroscopy tool. A battery module powers the tool. A memory controller module provides processing power and memory for storing spectroscopy data. A pulsed-neutron gamma-ray spectroscopy module has a pulsed-neutron source and a gamma- ray detector system to detect gamma-rays released when neutrons from the pulsed-neutron source interact with the matter in and around the wellbore.

Description

E UNITED STATES PATENT AND TRADEMARK RECEIVING OFFICE A PATENT COOPERATION TREATY APPLICATION ON:

SYSTEM AND METHOD FOR MEMORY PULSED-NEUTRON GAMMA-RAY SPECTROSCOPY LOGGING

INVENTED BY:

JEROME A. TRUAX

HOUSTON, TX 77077 CITIZENSHIP: U.S.

DONALD L. CRAWFORD

SPRING, TX 77379 CITIZENSHIP: U.S.

DANIEL F. DORFFER

HOUSTON, TX 77079 CITIZENSHIP: U.S.

CLIVE D. MENEZES

CONROE, TX 77384 CITIZENSHIP: U.S. SYSTEM AND METHOD FOR MEMORY PULSED-NEUTRON GAMMA-RAY SPECTROSCOPY LOGGING

BACKGROUND

Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information typically includes characteristics of the earth formations traversed by the borehole, along with data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as "logging", can be performed by several methods.

In conventional "wireline" logging, a probe (or "sonde") containing formation sensors is lowered into the borehole after some or all of the well has been drilled. The formation sensors are used to determine certain characteristics of the formations traversed by the borehole. The upper end of the sonde is attached to a conductive wireline that suspends the sonde in the borehole. Power is transmitted to the instruments in the sonde through the conductive wireline. Conversely, the instruments in the sonde communicate information to the surface using electrical signals transmitted through the wireline.

One wireline-logging technique for measuring formation density employs gamma rays. Gamma rays are high-energy photons emitted from an atomic nucleus. Such radiation is typically associated with the decay of radioactive elements. One example of an existing logging instrument for measuring density includes a gamma-ray source of cesium- 137. The gamma rays from the source travel into the formation where they interact with electrons. The interactions include absorption and scattering. Some of the scattered gamma rays return to detectors in the logging instrument where they are counted and their energy is measured. From the gamma-ray measurements, a determination of electron density and lithology type may be made. From these determinations, a standard weight-to-volume density may be calculated.

Closely related techniques for performing porosity measurements involve the use of neutron tools. Neutrons emitted from a neutron source interact with the environs, including the formation, and are absorbed, or scattered back to detectors in the tool. From the neutron detector measurements, a determination of formation porosity may be calculated.

- 1 - In each case, a specially trained operator is necessary at the surface to supervise the data collection. As the price of oil increases, old oil fields are getting second and third looks, but without indications of success, the cost to setup and collect wireline data may be prohibitive.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which:

Fig. 1 shows a representative wireline-logging configuration;

Fig. 2 shows a representative slickline configuration;

Fig. 3 shows one modular memory downhole logging tool cartridge embodiment;

Fig. 4 shows one battery module embodiment;

Fig. 5 shows one memory controller module embodiment;

Fig. 6 shows a representative pulsed-neutron source;

Fig. 7 shows a representative timing diagram for the pulsed-neutron source;

Fig. 8 shows a flowchart of an embodiment of a method of operation of the modular slickline downhole logging tool cartridge;

Figs. 9a-9d show graphs of representative data;

Fig. 10 shows a representative logging-while-drilling (LWD) configuration; and

Fig. 11 shows a representative through-bit logging configuration.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components and configurations. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion

- 2 - and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to...". Also, the term "couple" or "couples" is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. The terms upstream and downstream refer generally, in the context of this disclosure, to the transmission of information from subsurface equipment to surface equipment, and from surface equipment to subsurface equipment, respectively. Additionally, the terms surface and subsurface are relative terms. The fact that a particular piece of hardware is described as being on the surface does not necessarily mean it must be physically above the surface of the earth; but rather, describes only the relative placement of the surface and subsurface pieces of equipment.

DETAILED DESCRIPTION

Accordingly there are disclosed herein a modular, battery-powered, memory pulsed- neutron gamma-ray spectroscopy downhole tool and methods suitable for slickline logging. A battery module powers the tool. A memory controller module provides processing power and memory for storing logging data. A pulsed-neutron gamma-ray spectroscopy module has a pulsed-neutron source and a gamma-ray detector system configured to detect gamma rays released when neutrons from the pulsed-neutron source interact with the matter in and around the wellbore. The logging tool is automated and includes one or more safety provisions to ensure that the pulsed-neutron source is disabled when personnel are present.

Turning now to the figures, Fig. 1 shows a representative well during wireline logging operations. As shown, a drilling platform 2 is equipped with a derrick 4 that supports a hoist 6 above a well head 12. In well bore 20, a wireline logging sonde 38 is suspended from a wireline cable 40 that optionally communicates power and telemetry between the sonde 38 and a logging truck 42. Alternatively, sonde 38 may include one or more battery-powered instruments that gather logging data and store it in internal memory. The wireline logging sonde 38 measures properties of formations 34 as the sonde traverses through the borehole. Skilled personnel in the logging truck are able to view and analyze the logging data in near-real time. Wireline logging is commonly employed to gather logs for newly-drilled boreholes, though it may also be employed for cased-hole logging.

- 3 - For existing wells, particularly wells that have been previously produced and are being considered for secondary recovery operations, slickline logging is an inexpensive (and hence preferred) logging technique. A slickline is usually a single strand of metal wire without any metal armor or protective covering, yielding a small-diameter wire (most commonly 0.108" or 0.125" in diameter). The lack of power transmission through the slickline limits slickline work to mechanical action, battery-powered gauges, and placing or retrieving items from the borehole. When the single strand of metal wire has insufficient strength, a braided wire is used. For purposes of this disclosure, the term slickline is distinguished from wireline by the lack of transmitted power and not the size of the cabling.

Fig. 2 shows a representative well during slickline logging operations. A tripod 58 or other suspension assembly is quickly erected over the well to raise and lower a slickline downhole tool cartridge 80 into the well. The downhole cartridge is suspended from a slickline 85. Typically, the slickline downhole tool cartridge 80 is lowered to the bottom of the region of interest and subsequently pulled upward at a constant speed. During the upward trip, sensors in the slickline downhole tool cartridge 80 perform measurements on the formations 34 adjacent to and in the borehole as the tool cartridge passes by.

For clarity, the following description will focus on embodiments of a modular memory pulsed-neutron gamma-ray spectroscopy tool. The principles described will apply equally well to other modular memory data-collecting tools, though minor changes to the details will be needed to accommodate the different implementation. Any such changes are expected to be readily perceived by those of ordinary skill in the art informed by this disclosure.

Fig. 3 shows one embodiment of a modular memory logging tool cartridge 300, which may be used as the slickline downhole tool cartridge 80 shown in Fig. 2. As shown, the modular memory logging tool cartridge 300 includes a battery module 310, a memory controller module 320, a pulsed-neutron gamma-ray spectroscopy module 330, an optional tool module 340, and an end plug 350. Generally speaking, the battery module 310 provides power to the other modules that need power. The memory controller module 320 is configured to store gamma-ray data from the pulsed-neutron gamma-ray spectroscopy module 330. The pulsed-neutron gamma-ray spectroscopy module 330 includes a pulsed-neutron source 334 and one or more photon detectors 332. In the illustrated embodiment, a plurality of photon detectors 332 is shown, with the

- 4 - detector 332 farthest from the pulsed-neutron source 334 being the "far" detector and the detector 332 nearest the pulsed-neutron source 334 being the "near" detector.

In various embodiments, the battery module 310 is configured to provide a plurality of operating voltages to the various modules 320-340. In another embodiment, the memory controller module 320 is further programmed to safely control the pulsed-neutron gamma-ray spectroscopy module 330 and possibly any optional modules, such as the optional tool module 340. Note that use of the optional tool module 340 allows for a plurality of data measurements to be taken simultaneously and/or concurrently. In various embodiments, the optional tool module 340 includes one or more of production logging tools, cement evaluation tools, and/or casing inspection tools. In various embodiments, the optional tool module 340 is placed between the battery module 310 and the location of the pulsed-neutron gamma-ray spectroscopy module 330. In other embodiments, there are multiple optional tool modules 340, located either before and/or after the location of the pulsed-neutron gamma-ray spectroscopy module 330.

Pulsed-neutron devices use induced gamma spectroscopy and decay time measurements to determine primarily oil saturation in reservoirs. For those having low (less than 20,000 ppm NaCl), high salinity or unknown salinity-formation water the inelastic, or C/O (carbon/oxygen) ratio, mode is used. For higher salinities the capture mode is used. Additionally, elemental analyses from the measured spectra identify lithology in all types of reservoirs using either operating mode.

Neutrons emitted by the pulsed-neutron source 334, or other neutron generator, interact with the borehole and formation environment following the burst. After collision with these neutrons, atomic nuclei emit gamma rays of distinct energies at characteristic times depending upon their atomic number. Within the first tens of microseconds, high-energy inelastic collisions occur. Gamma rays emitted in this period are important for C/O ratio measurements, but of lesser interest for capture logging. From this time on to about 1 ms or longer, the neutrons are slowed and become low energy thermal (or epithermal) neutrons, which are captured. A capture event occurs upon collision with certain nuclei in the environment and leads to the emission of a gamma ray. The rate of such capture is a result of thermal neutron collisions mainly with hydrogen and chlorine. Some of the instabilities created by neutron collisions may take, numerous seconds, minutes, or longer to return to normal. Gamma rays emitted at such times are

- 5 - of little use in capture logging, but are important for oxygen activation water movement logs or silicon activation gravel pack logs.

In one embodiment, the pulsed-neutron gamma-ray spectroscopy module 330 includes two sodium iodide (thallium doped) detectors 332, as are known in the art. The pulsed-neutron gamma-ray spectroscopy module 330 also includes the photomultiplier tubes and associated electronics, including high voltage power supply, etc., as are well known in the art. In this embodiment, data collection preferably is in the capture mode. The physics of capture mode pulsed-neutron gamma-ray spectroscopy is well known.

In another embodiment, the pulsed-neutron gamma-ray spectroscopy module 330 includes two BGO detectors 332, as are known in the art. The pulsed-neutron gamma-ray spectroscopy module 330 also includes the photomultiplier tubes and associated electronics, including high voltage power supply, etc., as are well known in the art. In this embodiment, data collection preferably is in the inelastic scattering mode. The physics of inelastic scattering mode pulsed-neutron gamma-ray spectroscopy is well known. Additional embodiments suing other neutron interaction modes are also contemplated.

Fig. 4 shows one embodiment of the battery module 310. As shown, a plurality of batteries 410A and 410B are shown, although different embodiments of the present invention may have different numbers of batteries. The batteries 410 are coupled to provide power to other modules 320-340 through power lines 425(A-C). Power line 425 A is shown at the battery 410 voltage. A plurality of DC/DC converters 415A, 415B are shown converting the battery voltage to other voltages for power lines 425B and 425C, respectively, although different embodiments of the present invention may have different numbers and types of power lines 425. In various embodiments, the memory controller module 320 operates on power line 425A. In various embodiments, the pulsed-neutron gamma-ray spectroscopy module 330 operates on power line 425B. In various embodiments, the optional tool module 340 operates on power line 425B or 425 C. Other power requirement embodiments are contemplated. Depending on power requirements as well as temperature and pressure downhole, the batteries 410 may be lithium ion, silver oxide, or even alkaline cells. Other battery types are contemplated. In an embodiment with three lithium ion battery sticks of 8 DD cells each, 600 A-hrs of power are available at a nominal 30 V, with 350 mA continuous and up to 2000 mA peaks.

- 6 - Fig. 5 shows one embodiment of the memory controller module 320. As shown, a memory controller 500 receives programming through a USB (universal serial bus) port 502 and power through power line 425A. The memory controller 500 also receives power line 425B into a safety switch 515, which directs power line 425B through an interface 550 coupled to transmit and receive data on signal line 525 from the pulsed-neutron gamma-ray spectroscopy module 330 and possibly the optional tool module 340. The programming port 502 is shown as USB, but could use any protocol as desired.

As shown in Fig. 5, the memory controller 500 also includes a plurality of processors 510A and 510B for controlling the operations of the memory controller. As shown, processor 510A receives programming instructions from the USB port 502 for controlling the operations of the memory controller, including access to the memory 520. Processor 510B is coupled to receive instructions from the processor 510A and control the safety switch 515, based on values from one or more sensors 505. The sensors 505 may receive input through ports 506, which are preferably analog data ports 506. In one embodiment, the sensors 505 include a temperature sensor, a pressure sensor, and an X-Y accelerometer. In various embodiments, the sensors 505 may include a casing collar locator (CCL), as is well known in the art.

In one embodiment, the safety switch 515 does not pass power on power line 425B until the pressure sensor 505 reads above a pre-determined value indicative of a depth of greater than about 200 feet (about 61 meters). In another embodiment, a plurality of pre-determined sensor values is required before the safety switch 515 will pass power on power line 425B. In one embodiment, the processors 510A and 510B are the same processor. In another embodiment, there are additional processors 510. In one embodiment, the memory controller 500 is a commercially available universal memory controller.

In the embodiment shown in Fig. 5, the interface 550 is a "personality module" designed to translate between data formats for the memory controller 500 and for the pulsed-neutron gamma-ray spectroscopy module 330 and/or the optional tool module 340. As such, in some embodiments, the interface 550 is optional. The memory 520 is preferably flash memory, along with any required interface hardware (and/or firmware/software) but other memory types are contemplated. Data are stored in the memory 520 in a standard wireline format, but any desired

- 7 - data format may be used. In one embodiment, the memory 520 is 6 GB. In another embodiment, the memory 520 is 12 GB. In additional embodiments, the size of the memory 520 differs.

Fig. 6 shows an embodiment of the pulsed-neutron source 334 of the pulsed-neutron gamma-ray spectroscopy module 330, the components of the source 334 are well known in the art. As shown, the high voltage source 610 receives power from power line 425B, is surrounded by sulfur hexafluoride 630, and provides a high voltage to the generator tube 620. The neutron generator tube 620 produces 14 MeV neutrons in a generally isotropic manner when an ionized deuterium is accelerated to high velocity (by the high- voltage power supply 610) and then collides with a tritium, resulting in an alpha particle and a 14 MeV neutron. The generator is pulsed at 10 kHz to produce large numbers of neutrons in short bursts for the inelastic scattering mode. In the capture mode, it is pulsed at 800 Hz. In various embodiments, commercially available pulsed-neutron sources, as are well known in the art for downhole logging, are used as the pulsed-neutron source 434.

Fig. 7 shows a representative timing sequence for the pulsed-neutron gamma-ray spectroscopy module 330. In one embodiment, the timing sequence 700 repeats continuously while logging occurs, with an overall period 725 of generally 25 ms. Each period 725 may be divided into a neutron source period 715 and a neutron off period 720. The neutron source period 715 is generally 20 ms. The neutron off period 720 is typically 5 ms. The neutron source period 715 is divided into a neutron production period 705 and a decay period 710. Neutron production period 705 is typically 80 μs in inelastic scattering mode and 20 μs in capture mode. In various embodiments, for each overall period 725, the timing period 715 repeats 16 times for capture mode and 200 times for inelastic scattering mode.

Fig. 8 shows a flowchart of an embodiment of a method 800 of operation of the memory logging tool cartridge 300. The illustrated method starts with configuring a downhole tool with one or more safety mechanisms 802. These safety mechanisms may include pressure sensors, temperature sensors, timers, position sensors, downlink commands, etc. or a plurality of these in any combination. The safety mechanisms include those associated with safety switch 515. The method 800 includes programming the tool at a central location outside the wellbore 804. In another embodiment, the central location is at the surface next to the well. In other embodiments, the central location is in other locations.

- 8 - The method 800 includes transporting the tool to the well from the central location 806 and lowering the programmed tool into the wellbore 808. The lowering 808 is performed in various embodiments by slickline, by wireline, through-bit, on the end of tubing, or by other means. The method 800 includes the tool automatically starting when a safety mechanism has an indication that the tool can be used safely 810. The safety mechanism in 810 is the same safety mechanism in 802. The method 800 includes operating the tool on battery power 812. In one embodiment, the entire tool is operated on battery power. In another embodiment, the neutron generator is powered by the batteries.

The method 800 includes storing data in a memory internal to the tool 814. In one embodiment, the memory and the data collecting portion of the tool are powered by the battery in 810 as well. In other embodiments, the memory is powered by wireline. Once the data are stored in the memory 814, the method includes removing the tool from the wellbore to the surface 816.

The method includes returning the tool to a central location 818. The method also includes downloading the data from the internal tool memory 820. In one embodiment, the central location for programming the tool 804 is the same central location for downloading the data from the memory 820. In another embodiment, the central location for programming the tool 804 is not the same central location for downloading the data from the memory 820.

In various embodiments, the method 800 omits certain steps. In one embodiment, the data are downloaded from the internal memory 820 without removing the tool from the well 816, even though the tool could have been removed from the well before downloading the data from the internal memory.

Figs. 9a-9d show exemplary data sets from the capture and the inelastic scattering modes, other sensor data, and resulting data. Figs. 9a and 9b are of inelastic scattering mode, while Figs. 9c and 9d are of capture mode.

The abbreviations used in Fig. 9a include PEA for peak, LIRI for lithography inelastic ratio, COIR for carbon oxygen inelastic ratio, FE for iron, CL for chlorine, CAPT for capture, INEL for inelastic, and SIGMA for the standard deviation. The abbreviations used in Fig. 9b include GR for natural gamma ratio, SIGMA FORM for the capture cross section, OAI for the oxygen activation, K for k-shell, STUN for the statistical uncertainty, YH for hydrogen yield,

- 9 - YSI for silicon yield, YCA for calcium yield, IRIN for the ration of inelastic scattering of nitrogen to fluorine, and RCAP for the ratio of the capture count rates. Note that when the LIRI is the left of the COIR, then oil is likely present. Similar abbreviations are used in Figs. 9c and 9d. The data charts shown in Figs. 9a-9d and all abbreviations used will be understood by those of skill in the art.

The logging tool assemblies disclosed above may be particularly suitable for tubing- conveyed logging or through-bit logging. Before describing through-bit logging, we begin with a discussion of the drilling process. Fig. 10 shows a representative well during the drilling process. As shown, a drilling platform 2 is equipped with a derrick 4 that supports a hoist 6. Drilling of oil and gas wells is carried out with a string of drill pipes connected together by "tool" joints 7 so as to form a drill string 8. The hoist 6 suspends a kelly 10 that is used to lower the drill string 8 through rotary table 12. Connected to the lower end of the drill string 8 is a drill bit 14. The bit 14 is rotated by rotating the drill string 8 or by operating a downhole motor near the drill bit. The rotation of the bit 14 extends the borehole.

Drilling fluid is pumped by recirculation equipment 16 through supply pipe 18, through drilling kelly 10, and down through the drill string 8 at high pressures and volumes to emerge through nozzles or jets in the drill bit 14. The drilling fluid then travels back up the hole via the annulus between the exterior of the drill string 8 and the borehole wall 20, through the blowout preventer (not specifically shown), and into a mud pit 24 on the surface. On the surface, the drilling fluid is cleaned and then recirculated by recirculation equipment 16. The drilling fluid cools the drill bit 14, carries drill cuttings to the surface, and balances the hydrostatic pressure in the rock formations.

Often, a downhole instrument sub 26 is coupled to a telemetry transmitter 28 that communicates with the surface to provide telemetry signals and receive command signals. A surface transceiver 30 may be coupled to the kelly 10 to receive transmitted telemetry signals and to transmit command signals downhole. One or more repeater modules 32 may be provided along the drill string to receive and retransmit the telemetry and command signals. The surface transceiver 30 is coupled to a logging facility (not shown) that may gather, store, process, and analyze the telemetry information.

- 10 - For through-bit logging, the drillstring 8 is raised partway out of the hole and an instrument sonde is lowered through the interior of the drill string and extended through a port in the bit 14 as shown in Fig. 11. (Various through-bit logging configurations are described in detail in co-pending Provisional US Patent Applications 60/885839, 60/885828, 60/885800, and 60/885761.) In this manner, open hole logging can be performed without completely removing the drillstring from the borehole. In some embodiments, the instrument sonde 36 may include sensor pads on centralizer arms 34. In one embodiment, the instrument sonde 36 includes a battery-powered pulsed neutron gamma-ray logging module as described above.

Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

- 11 -

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A modular memory downhole tool cartridge, comprising: a battery module; a memory controller module powered from the battery module, wherein the memory controller module includes at least one memory and one or more processors to store pulsed- neutron gamma-ray spectroscopy data from the pulsed-neutron gamma-ray spectroscopy module in the at least one memory; and a pulsed-neutron gamma-ray spectroscopy module powered from the battery module, wherein the pulsed-neutron gamma-ray spectroscopy module includes a pulsed-neutron source and a photon detector system to detect photons released when neutrons from the pulsed-neutron source interact with matter and to provide the pulsed-neutron gamma-ray spectroscopy data to a processor of the one or more processors.

2. The modular slickline downhole tool cartridge of claim 1, wherein the battery module includes one or more batteries and one or more voltage converters, wherein at least one of the one or more voltage converters is to provide power at a first operating voltage to the pulsed-neutron gamma- ray spectroscopy module.

3. The modular slickline downhole tool cartridge of claim 2, wherein the battery module to provide a plurality of differing operating voltages to various ones of the plurality of modules.

4. The modular slickline downhole tool cartridge of claim 3, wherein the battery module to provide differing operating voltages to the memory controller module and the pulsed-neutron gamma-ray spectroscopy module.

5. The modular slickline downhole tool cartridge of claim 1, wherein the memory controller module further includes one or more sensors and at least one safety switch coupled to at least one of the one or more sensors, wherein the at least one safety switch is coupled to receive power from the battery module to at least the pulsed-neutron gamma-ray spectroscopy module, wherein the at least one safety switch to pass operating power to the pulsed-neutron gamma-ray spectroscopy module only when the at least one of the one or more sensors provides an indication of a pre-defined safe condition to the at least one safety switch.

6. The modular slickline downhole tool cartridge of claim 1, further comprising:

- 12 - an additional downhole tool module including at least one additional downhole sensor tool; and wherein a voltage converter of the one or more voltage converters is coupled to provide power to the additional downhole tool module, and wherein a processor of the one or more processors is coupled to store data from the additional downhole tool module in memory locations of the at least one memory.

7. The modular slickline downhole tool cartridge of claim 1, wherein at least one of the one or more processors to accept programming at the surface.

8. The modular slickline downhole tool cartridge of claim 7, wherein the at least one of the one or more processors further execute the programming in response to a pre-determined indication from one or more of the at least one sensors.

9. A modular memory downhole tool cartridge, comprising: a battery module; a memory controller module powered from the battery module, wherein the memory controller module includes a memory and a processor to store collected data in the memory; and a data-collecting module powered from the battery module, wherein the data-collecting module provides the collected data to the processor.

10. The modular memory downhole tool cartridge of claim 9, further comprising: a safety mechanism that prevents power to at least a portion of the data-collecting module until a predetermined sensor value is reached.

11. The modular memory downhole tool cartridge of claim 9, wherein the battery module further comprises one or more power converters providing differing power to the memory controller module and the data-collecting module.

12. A slickline logging method that comprises: lowering a pulsed-neutron gamma-ray logging tool into a well on a slickline cable; and collecting logging data as the logging tool travels along the well.

13. The method of claim 12, further comprising: storing the logging data in internal tool memory.

14. The method of claim 13, wherein the method further comprises:

- 13 - configuring operational parameters of the logging tool at a central location before transporting the logging tool to the well site for said lowering and collecting operations.

15. The method of claim 14, further comprising: returning the logging tool to the central location before retrieving said logging data from said internal memory.

16. The method of claim 13, wherein said lowering includes: extending said logging tool through a port in a drill bit in said well.

17. The method of claim 13, wherein the logging tool is battery powered.

18. The method of claim 13, wherein the slickline cable has no conductive armor.

19. The method of claim 13, wherein the logging tool includes at least two different types of safety mechanism to prevent operation of a pulsed-neutron source near personnel.

20. A logging method that comprises: equipping a pulsed-neutron gamma-ray logging tool with at least one safety mechanism configured to prevent operation of a pulsed-neutron source within a predetermined distance of the surface; and lowering the logging tool into a well on a cable having a diameter of no more than 0.2 inches.

21. The method of claim 20, wherein the cable has no conductive armor.

22. The method of claim 20, further comprising: retrieving the logging tool from the well; and downloading pulsed-neutron gamma-ray spectroscopy logs from a memory module coupled to the logging tool.

23. The method of claim 20, wherein the at least one safety mechanism includes a pressure sensor.

24. The method of claim 20, wherein the at least one safety mechanism includes a timer.

- 14 -