Search

EP-3791216-B1 - GEOLOGIC FORMATION NEUTRON POROSITY SYSTEM

EP3791216B1EP 3791216 B1EP3791216 B1EP 3791216B1EP-3791216-B1

Inventors

  • Abadie, Joan
  • SALEHI, MOHAMMAD TAGHI
  • ITO, KOJI
  • RASMUS, JOHN
  • HONG, Xiao Bo

Dates

Publication Date
20260506
Application Date
20190510

Claims (15)

  1. A computer-implemented method (1100) comprising: receiving neutron data and density data for a high angle borehole in a geologic formation (1114, 1118), wherein the received neutron data comprises smearing due to the high angle of the borehole with respect to a layer of the geographical formation; determining a migration length value for the layer of the geological formation (1120) based on the received neutron data; forward modeling at least the layer of the geological formation based at least in part on the migration length value and the density data (1130); and outputting, based at least in part on the forward modeling, modeled neutron data for the layer of the geological formation (1140).
  2. The method of claim 1 wherein the determining the migration length value accounts for the geometry of the borehole.
  3. The method of claim 1, wherein the determining the migration length value comprises implementing an iterative loop and one or more stopping criteria.
  4. The method of claim 1, wherein the determining the migration length value comprises implementing a dichotomic search.
  5. The method of claim 1 wherein the determining the migration length value comprises forward modeling of at least one of: best thermal neutron porosity and thermal neutron porosity at least for the layer of the geological formation.
  6. The method of claim 1 wherein the neutron data comprises best thermal neutron porosity data or thermal neutron porosity data.
  7. The method of claim 1, comprising simulating physical phenomena in the geological formation based at least in part on the output modeled neutron data for the layer of the geological formation.
  8. The method of claim 1, wherein the neutron data comprises logging while drilling data acquired by a downhole tool during a drilling operation in the geologic formation.
  9. The method of claim 1, wherein the receiving comprises receiving the neutron data from a logging while drilling tool during a drilling operation.
  10. The method of claim 9, further comprising controlling the drilling operation based at least in part on the modeled neutron data, wherein controlling comprises directing a drill bit with respect to a reservoir in the geological formation and wherein the modeled neutron data represent porosity characteristics of the reservoir.
  11. The method of claim 1, further comprising rendering a graphical user interface to a display wherein the graphical user interface comprises a representation of a model of at least a portion of the geological formation and a representation of at least a portion of the high angle borehole, wherein the graphical user interface comprises graphical tools for adjusting one or more boundaries of one or more layers of the geological formation.
  12. The method of claim 1, further comprising determining hydrocarbon saturation based at least in part on the modeled neutron data for the layer of the geological formation.
  13. The method of claim 7, further comprising issuing a signal to at least one piece of equipment that interacts with the geologic al formation.
  14. A system (250) comprising: a processor (256); memory (258) operatively coupled to the processor; and processor-executable instructions (270) stored in the memory to instruct the system to perform the steps of the method of any preceding claim.
  15. One or more computer-readable storage media comprising computer-executable instructions executable to instruct a computing system to perform a method according to any of claims 1 to 13.

Description

BACKGROUND A geologic formation is formed of material, which can include material as a matrix that can include one or more other materials such as, for example, fluids, solids, etc. A geologic formation can include pores within a material matrix that define a porosity that may be occupied by material (e.g., fluid, etc.). Porosity may be determined based on an effect of a formation on fast neutrons emitted by a source. For example, hydrogen can have an effect on a neutron that slows the neutron down and captures the neutron. As hydrogen may be present predominantly in pore fluid, a neutron porosity log responds predominantly to porosity; noting that other factors can include formation matrix factors, fluid factors, chemical factors, geometric factors, etc. A log may be calibrated with assumptions as to a type of matrix (e.g., limestone, sandstone, dolomite, etc.) and type of pore fluid (e.g., pores filled with a known material such as fresh water). Porosity may be presented in units of porosity (vol/vol or p.u.) for a matrix chosen. Another approach presents neutron data in counts per second or American Petroleum Institute (API) units. A depth of investigation of a neutron measurement may be of the order of centimeters to tens of centimeters (e.g., 2 cm to 40 cm, etc.). Neutron measurements may be based on phenomena such as thermal or epithermal neutron detection. Thermal neutrons tend to have about the same energy as surrounding matter (e.g., less than approximately 0.4 eV), while epithermal neutrons tend to have higher energy (e.g., between approximately 0.4 and approximately 10 eV). Precision tends to increase with higher count rates, which tend to occur at low porosity. Neutron measurements can be utilized in interpretation. Interpretation is a process that involves analysis of data to identify and locate various subsurface structures (e.g., horizons, faults, geobodies, etc.) in a geologic environment. Various types of structures (e.g., stratigraphic formations) may be indicative of hydrocarbon traps or flow channels, as may be associated with one or more reservoirs (e.g., fluid reservoirs). In the field of resource extraction, enhancements to interpretation can allow for construction of a more accurate model of a subsurface region, which, in turn, may improve characterization of the subsurface region for purposes of resource extraction. Characterization of one or more subsurface regions in a geologic environment can guide, for example, performance of one or more operations (e.g., field operations, etc.). WO 2012/162404 A2 describes a computer-implemented method for simulating a response of a neutron well logging instrument including defining a function of neutron migration length with respect to expected radiation detector counting rate for selected values of formation porosity, the function being related to neutron slowing down and neutron diffusion lengths and being weighted for formation density. An expected radiation detector counting rate is calculated using the defined function based on an initial estimation of formation porosity and density. US 5377105 describes a method of deconvolving the far-spaced detector response of a dual-spaced neutron logging tool, coupled with dynamic matching of the near-spaced detector response to improve the vertical resolution of the tool's formation porosity measurements. US 2017/160425 A1 describes a method for determining at least one property of a geological formation that employs at least one forward model to derive at least one synthetic detector measurement that relates to neutron-induced gamma-ray emission from geological formation. The forward model is also used to infer at least one property of the geological formation including bulk density of the geological formation. SUMMARY The present invention resides in a method as defined in claim 1, in a system as defined in claim 14 and in one or more computer-readable storage media as defined in claim 15. BRIEF DESCRIPTION OF THE DRAWINGS Features and advantages of the described implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings. Fig. 1 illustrates an example system that includes various components for modeling a geologic environment and various equipment associated with the geologic environment;Fig. 2 illustrates an example of a sedimentary basin, an example of a method, an example of a formation, an example of a borehole, an example of a borehole tool, an example of a convention and an example of a system;Fig. 3 illustrates an example of a technique that may acquire data;Fig. 4 illustrates examples of equipment including examples of downhole tools and examples of bores;Fig. 5 illustrates examples of equipment including examples of downhole tools;Fig. 6 illustrates an example of forward modeling and inversion as to seismic data and an Earth model of acoustic impedance;Fig. 7 illustrates an example graphical user interface