Radiant energy – Geological testing or irradiation – Well testing apparatus and methods
Reexamination Certificate
2001-09-21
2004-07-27
Hannaher, Constantine (Department: 2878)
Radiant energy
Geological testing or irradiation
Well testing apparatus and methods
Reexamination Certificate
active
06768106
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates generally to exploration and production, and more particularly, to a method and apparatus for monitoring and detecting kicks and cuttings-bed formation or drill cuttings “pack-off” while drilling.
2. Background Art
The characteristics of geological formations are of significant interest in the exploration for and production of subsurface mineral deposits, such as oil and gas. Many characteristics, such as the hydrocarbon volume, porosity, lithology, and permeability of a formation, may be deduced from certain measurable quantities. Among these quantities are the non-invaded resistivity, flushed zone resistivity, and diameter of invasion in a formation. In addition, the resistivity of the mud mixture and the distance from the tool face to the formation through the mud can be determined with resistivity measurements. The quantities are typically measured by logging-while-drilling (“LWD”) and wireline tools. The tool carries one or more sources that radiate energy into the formation and receivers that sense the result of the radiation. The detectors measure this result and either transmit the data back uphole or temporarily store it downhole. Typically, once uphole, the data is input to one or more formation evaluation models, which are typically software programs used to evaluate the geological formation from which the data was gathered. Also, the effect of the mud mixture present in front of the tools, between the tool and the formation which is to be evaluated, is typically considered as an undesirable borehole effect, for which measurements have to be corrected.
Formation evaluation models usually assume thick beds within the formation that lie normal to the wellbore. These beds are also assumed to be homogeneous not only in composition, but in structure in all azimuths about the wellbore. Logging tools were traditionally designed and built with these assumptions as a guide. These assumptions simplified modeling the formations, which is valuable from the perspective of computing resources.
Formation evaluation models typically give little regard to the side of the borehole on which the tools measure or to whether the tools are azimuthally focused, because formation properties in all directions are assumed to be the same. This is not a problem in thick beds with bedding normal to the wellbore, i.e., in situations where the formation structure actually matches the assumptions. When the bed is no longer normal to the wellbore, however, the measurements can become quite different from one side of the borehole to the other. Without processing, it is impossible to obtain accurate results when combining azimuthally focused measurements (e.g., a wireline or logging while drilling density measurement) and azimuthally omni-directional measurements (e.g., a wireline or logging while drilling induction resistivity measurement). The azimuthally focused tool may respond to one bed while the azimuthally non-focused tool responds to the average of multiple beds. The geometrical effects of dip must be removed before meaningful processing can proceed.
Fluid distribution is another area that many models ignore. In permeable, dipping formations, invasion of drilling fluid is often asymmetric because of gravity slumping of the filtrate. (“Dipping” is used herein as a relative term which concerns the relative angle between the wellbore and the bedding plane.) More rigorous two-dimensional interpretation models do include filtrate invasion, but ignore dipping beds and azimuthal variations of the invasion. Azimuthal variations are generally not of concern in vertical wells with bedding normal to the wellbore. However, they become important as beds begin to dip or the well becomes deviated. Such variations can be due to dip and asymmetric filtrate invasion.
Gravity also complicates an evaluation. It segregates invading filtrate from formation fluids if there is a density difference. This is especially pronounced in gas zones with large density contrast. Differential pressure between the mud column and the formation creates the initial invasion, normal to the wellbore. This invasion penetrates the formation only so far before gravity dominates at which point the majority of filtrate begins to flow downward rather than outward. “Down” does not have to mean toward the bottom of the hole; it could mean toward one of the sides of the hole, if that is the down direction of the bedding. The higher the vertical permeability the more obvious this effect. The heavier fluid will puddle at the first impermeable layer. This puddling can appear on wireline logs (and LWD logs if sufficient time has elapsed since drilling) as an apparent water leg at the base of thick, highly permeable gas zones, even though those zones produced dry gas.
In vertical wells, thin, low permeability layers, which minimize segregation, often mask the effect. If the spacing between layers is less than the axial resolution of the logging tool, then they will not be detectable. In the case of dipping beds, the segregation effect is more obvious. All of the filtrate that leaves the well eventually migrates down dip, even the filtrate that leaves on the up-dip side of the wellbore. This increases the depth of invasion in one direction, making it more obvious on deeper reading logging tools and it creates azimuthal variations of fluids.
Thus, formation evaluations of deviated wells and wells with dipping beds are a challenge, especially with gas reservoirs. Log responses in these wells are often considered “unexplainable.” Asymmetry, fluid distribution, and gravity contribute greatly to this problem because of the assumptions one-dimensional and two-dimensional formation evaluation models embody. Even calibration of logs to core samples can be difficult because of the dramatic changes from axial level to axial level asymmetry can cause.
In addition to evaluating the fluids in the formation, the fluids in the borehole are also of interest. As the degree of deviation of a well builds, there is a proportional increase in the likelihood of cuttings bed build-up in the well bore due to the effects of gravity. Cuttings beds have an adverse impact on the cuttings transport and the downhole pressure. Monitoring cuttings transport has been the subject of much research and has a direct impact on how specific well sections ought to be drilled. Gravity also has additional effects on mud mixtures in deviated wells. Particles in suspension in the mud (for instance barite), can fall out of suspension, and the mud mixture on the high side of the hole, can have different properties than the mud mixture on the low side of the hole. Therefore, if the cuttings and other materials are not maintained in suspension, the cuttings and other materials will rest on the low side of the hole, and the mud mixture, the cuttings and other materials will not be azimuthally homogeneously distributed across the borehole.
Currently, the borehole fluid (“drilling mud” or “mud”) is characterized at the surface and its properties are extrapolated to conditions downhole. Factors such as temperature, pressure, and mud composition can vary in both space and time along the borehole. In addition, new mud formulations are continually evolving in the industry.
U.S. Pat. No. 3,688,115, issued to Antkiw, discloses a fluid density measuring device for use in producing oil wells. Density is determined by forcing the well fluid to pass through a chamber in the device. The fluid attenuates a beam of gamma radiation that traverses the chamber, the relative changes in the beam intensity providing a measure of the density in question. Streamlined surfaces and passageways leading into and out of the chamber eliminate turbulent flow conditions within the measuring chamber and thereby establish the basis for a substantially more accurate log of the production fluid density.
U.S. Pat. No. 4,297,5
Cooper Iain M.
Gzara Kais
Hannaher Constantine
Jeffery Brigitte L.
McEnaney Kevin P.
Ryberg John H.
Schlumberger Technology Corporation
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