Thermal measuring and testing – Temperature measurement – Geophysical
Reexamination Certificate
2001-11-30
2004-09-14
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
Geophysical
C374S102000
Reexamination Certificate
active
06789937
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the prediction of formation temperatures in a subsurface formation and, more particularly, to the prediction of the temperature of a hydrocarbon formation temperature.
2. Description of Related Art
Hydrocarbon fluids, such as oil and natural gas, are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. An understanding of the undisturbed reservoir temperature is desirable for numerous applications involved in the drilling, completion and production of reservoir fluids. These applications may include, for example: drilling fluid and cement slurry design; log interpretations; corrosion tendencies in wellbore tubulars and downhole equipment; hydrocarbon reserve estimation; flow assurance design; and estimations of geothermal energy, etc.
In drilling operations, the formation temperature has a direct bearing on drilling fluid rheology and therefore has to be considered in drilling fluid and wellbore design. The formation temperature directly impacts cement dehydration and cure times, and therefore needs to be considered in the design of casing and cementing programs. The interpretation of electric logs requires accurate formation resistivities, which are dependent on temperature. In production and well-control operations, accurate computations of fluid flow rates are important. Fluid temperature, both as a function of depth and elapsed time, dictates fluid properties such as density and viscosity, and therefore influences the pressure drops and/or the maximum allowable production rates that can be achieved. Flow assurance design considerations, such as hydrate formation and paraffin deposition prevention, depend on an accurate knowledge of the reservoir temperature.
As a wellbore is drilled, a temperature disturbance is introduced by the circulating drilling fluids, thereby cooling the formation around the borehole. The initial undisturbed formation temperature exists only at a certain distance away from the wellbore. During the circulation of fluids, often referred to as “mud”, the temperature within the borehole drops and reaches a pseudo-steady state condition in a very short time. After a certain period of time, the temperature within the wellbore during fluid circulation can be considered constant. Earlier studies have indicated that a constant temperature difference between the bottom-hole fluid and wellbore wall is achieved almost immediately and maintained throughout the life of the wellbore fluid circulation process. This means that the heat transmission from the formation to the wellbore during wellbore fluid circulation is a constant heat flux dominated process. Therefore, during mud circulation, the heat transfer between the wellbore and the formation can be described with a constant heat flux solution of an infinite reservoir. See Raymond, L. R.: “
Temperature Distribution in a Circulating Drilling Fluid”
, JPT, March 1969; and Schoeppel, R. J., Bennet, R. E.: “
Numerical Simulation of Borehole and Formation Temperature Distributions While Drilling to Total Depth”
, SPE paper 3364, presented October 1971.
The amount of departure from the undisturbed formation temperature during drilling and completion operations depends upon several factors, such as, the original temperature distribution, the physical properties of the reservoir rock and the drilling/completion fluids. Fluid circulation rates and duration, and the tubular and cementation design used on the well are also factors that influence the temperature profile. Formation temperatures are often estimated by using temperature measurements taken inside the wellbore, often in conjunction with well logging and fluid sampling.
The process of formation fluid sampling typically involves the lowering of a sampling tool into the wellbore. The sampling tool collects one or more samples of formation fluid by the engagement between a probe module of the sampling tool and the wall of the wellbore. Embodiments of sampling tools may comprise more than a single probe, such as with dual-probe or multi-probe modules, enabling the sampling of differing sites within the formation within a single deployment of the sampling tool. There are several commercially available sample tools available, for example the Modular Dynamics Formation Tester (MDT™) made by Schlumberger, the Reservoir Characterization Instrument (RCI
SM
) from Baker Atlas, and the Reservoir Description Tool (RDT™) tool made by Halliburton.
The Modular Dynamics Formation Tester (MDT) formation testing tool, owned and provided by Schlumberger operates by creating a pressure differential across an engagement of a probe module with the wellbore to induce formation fluid flow into one or more sample chambers within the sampling tool. This and similar processes are described in U.S. Pat. Nos. 4,860,581; 4,936,139 (both assigned to Schlumberger). Due to the changes in the temperature field surrounding the wellbore discussed above, the temperature data acquired by the MDT is typically lower than the actual static formation temperature, because of short sampling time. One distinct feature of wireline pretest and sampling is that the flow regime is primarily controlled by three-dimensional (3-D) spherical or radial flow where the probe functions as a point sink. Therefore, the specific difficulty in determining the original formation temperature is the calculation of the fluid temperature at the probe during the recording, which is associated with 3-D spherical flow.
Another sampling tool is the Reservoir Characterization Instrument (RCI), provided by Baker Atlas. It can comprise an optical analyzer, named SampleView
SM
, that can be used to monitor contamination levels within sample formation fluids pumped through the tool, and can be run with other reservoir characterization sensors. Examples of other reservoir characterization sensors include pressure sensors and sensors that measure the apparent dielectric constant of the sample fluid, thereby distinguishing oil, gas and water within the sample fluids. The quality of a reservoir fluid sample and the time required to acquire the sample can be predicted utilizing a three-dimensional fluid flow simulation model and input data acquired from the RCI, such as formation pressure, formation permeabilities, and formation fluid properties.
Still another sampling tool that can be utilized with the present invention includes the Reservoir Description Tool (RDT) tool manufactured by Halliburton. It can comprise a modular apparatus that uses nuclear magnetic resonance (NMR) techniques for making downhole NMR measurements of the formation fluid samples, as described in U.S. Pat. No. 6,111,408 to Blades et al.
Referring to the attached drawings,
FIG. 1
illustrates a prior art representative drilling/production platform
10
having a tubular string
12
extending into a wellbore
14
. The wellbore
14
has penetrated subterranean formations
16
, and intersects a productive reservoir
18
. A casing string
20
lines the well and provides support and isolation of the wellbore
14
from the formations
16
and bodies of water
22
. Wellbore drilling or completion fluids
24
, commonly referred to as “mud”, are typically circulated down the tubular string
12
and up the wellbore
14
. The circulation of wellbore fluids
24
results in the cooling of the reservoir
18
around the wellbore
14
. Upon the cessation of fluid circulation, the tubing
12
can be removed from the wellbore
14
.
FIG. 2
illustrates a prior art representative drilling/production platform
10
having a downhole tool
26
inserted into the wellbore
14
on a wireline
28
. The downhole tool
26
can comprise a formation-testing tool capable of collecting one or more samples of formation fluid, such as, for example, the Modular Dynamics Formation Tester (MDT) formation-testing tool. In addition to obtaining a sample of the formation fluid coming from the reservoir
18
, the downhole tool
Cheng Yueming
Haddad Sammy
Echols Brigitte E.
Gutierrez Diego
Jagan Mirellys
Ryberg John
Salazar J. L. Jennie
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