Boring or penetrating the earth – With signaling – indicating – testing or measuring – Indicating – testing or measuring a condition of the formation
Reexamination Certificate
2002-06-17
2004-09-21
Suchfield, George (Department: 3672)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
Indicating, testing or measuring a condition of the formation
C073S152020, C073S152030, C166S254200, C175S065000, C507S103000, C507S129000, C507S130000, C507S135000, C507S136000, C507S240000, C507S248000, C507S260000, C507S904000
Reexamination Certificate
active
06793025
ABSTRACT:
BACKGROUND OF THE INVENTION
The use of wireline well logs is well known in the art of drilling subterranean wells and in particular oil and gas wells. A wireline log is generated by lowering a logging tool down the well on a wireline. The tool is slowly brought back to the surface and the instruments on the logging tool take measurements that characterize the formations penetrated by the well in addition to other important properties of the well. Electrical logs and other wireline log techniques are depended upon in the oil and gas exploration industry to determine the nature of the geology and the reservoir properties of the petroleum bearing formations penetrated by the well. Further, wireline well logs are often the only record of the formations penetrated by the well available for correlation amongst different wells in a particular field.
When an electrical wireline log is made of a well, electrodes on the well logging tool are in contact with wellbore fluid or filter cake and hence the formation rocks through which the well has penetrated. An electrical circuit is created and the resistance and other electrical properties of the circuit may be measured while the logging tool is retracted from the well. The resulting data is a measure of the electrical properties of the drilled formations verses the depth of the well. Another common measurement made with an electrical log, besides resistivity, is the spontaneous or self potential. One of skill in the art of well logging and electrical logging in particular should understand how to interpret the results of such measurements to determine the presence or absence of petroleum or gas, the porosity of the formation rock and other important properties of the well. Further information in this regard can be found in the book entitled “Essentials of Modern Open-hole Log Interpretation” by John T. Dewan the contents of which are hereby incorporated herein by reference, and other similar reference material.
An alternative or supplement to wireline logging involves logging tools placed in specialized drill collar housing and run in the drill string near the bit. This technique is known as logging-while-drilling (LWD) or formation-evaluation-while-drilling(FEWD). Measurements such as electrical resistivity can be thereby taken and stored down hole for later retrieval during a “tripping out” of the drill string, or transmitted to the surface via mud-pulse telemetry. Such techniques should be known to one of skill in the art of well drilling and subterranean well logging.
The use of oil-based muds and drilling fluids has become increasingly popular since their introduction of the technology in the 1950's. Innovations in oil-based muds and drilling fluids are of on-going importance with the development of environmentally friendly drilling fluids and fluids having other special characteristics. Oil-based muds offer advantages over water-based muds in many drilling situations. In particular, oil-based muds are known in the art to provide excellent shale inhibition, borehole stability, lubricity, thermal stability, tolerance of contamination and ease of maintenance. Despite the many benefits of utilizing oil-based muds and drilling fluids, they have disadvantages. One such disadvantage addressed by the present invention is that normal resistivity and self potential measurements cannot be taken when the well has been drilled with a conventional oil-based mud or drilling fluid due to the non-conductive nature of the oil-based drilling fluids and muds.
Oil-external microemulsion fluids containing sodium petroleum sulfonate are reported in the literature, for example see U.S. Pat. No. 4,012,329. A microemulsion is a thermodynamically stable dispersion of one liquid phase into another, stabilized by an interfacial film of surfactant. Microemulsions are typically clear solutions in which there is very low interfacial tension between the two phases. In the microemulsions of U.S. '329, sodium petroleum sulfonate forms micelles that contain water and clay such that the clay has to be added as a dispersion in water an cannot be added as dry powder. This procedure is necessary in order for the clay, barite and other water dispersible materials to be contained within the micelles of the microemulsion. This technology raises logistic issues such as two separate mixers, and makes it more difficult to adjust the mud density during the process of drilling a well. Devices which recycle drilling fluid by solid-separation of the weighting materials are not 100% efficient, and thus the mud density must be continuously adjusted.
There are additional differences between a microemulsion and a standard emulsion in thermodynamic stability as the standard emulsion droplets will eventually agglomerate and the dispersed phase will phase separate. Putting work into a standard emulsion, or increasing the surfactant concentration usually improves its stability, but this does not appear to be the case with microemulsions. Microemulsions are believed to be dependent on specific interactions among the constituent molecules and the interface. If the correct emulsifier is used and the other conditions are right, the microemulsion will likely form spontaneously, without additional mechanical work; however, energy input may decrease the time it takes to reach an equilibrium state. Standard emulsion droplet sizes are much larger, and result in a cloudy or milky dispersion. Additionally, the properties of the filtercakes formed by the microemulsion, as well as the properties of the fluid filtrate are different. Further, microemulsions tend to have lower conductivity than is needed for some modem logging operations.
Another disadvantage addressed by the present invention is maintaining conductivity over a long period of time. When these fluids and muds are exposed to air, a drop in conductivity occurs. Lime is typically used as a buffer for acidic gases, but begins to lose its effectiveness upon exposure of the fluids and muds to air. Of the many attempts to date, none have met with much success or commercial acceptance in the subterranean well drilling art. Thus there exists an on-going need and desire for drilling fluids and drilling muds that are oil-based and yet allow the taking of wireline electrical logs of the well and electrical-logging-while-drilling.
SUMMARY OF THE INVENTION
The present invention is generally directed to providing an oil-base medium suitable for electrically logging a subterranean well. The medium is an invert emulsion that in its continuous phase includes an oleaginous fluid, and an electrolytic salt. The medium additionally includes an emulsifier capable of forming a microemulsion and an emulsion capable of forming an invert emulsion. Thus, the medium, with water as the discontinuous phase, is an invert emulsion wherein the continuous phase is a microemulsion. The continuous phase is in contact with the logging tool and the wellbore of the well. The continuous phase may have dispersed within it fluid droplets or solid particles immiscible with the continuous phase. The oleaginous fluid may be a diesel, mineral oil, vegetable oil, synthetic oil, silicone oil, or combinations of these fluids. Additionally the logging medium may contain in its continuous phase a polar organic solvent. The polar organic solvent should be at least partially soluble in the oleaginous fluid, but should also have partial solubility in water. Examples of such polarsolvents may include ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and their alkyl ether derivatives. The electrolytic salt or brine should be selected so that it is at least partially soluble in the mixture of oleaginous fluid and polar organic solvent. Suitable salts or brines may include magnesium chloride, sodium chloride, sodium bromide, potassium chloride, ammonium chloride, calcium chloride, calcium bromide, organic salts or combinations thereof Organic salts may include salts such as sodium acetate, potassium acetate, sodium citrate, quaternary amine
Bell Reginald J.
Patel Arvind D.
Tehrani Ahmadi
Young Steve
Howrey Simon Arnold & White L.L.P.
M-I L. L. C.
Suchfield George
White Carter
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