Summary
With the recent development of temperature measurement systems such as
fiber-optic distributed temperature sensors, continuous temperature profiles in
a horizontal well can be obtained with high precision. Small temperature
changes with a resolution on the order of 0.1°F can be detected by modern
temperature-measuring instruments in intelligent completions, which may aid the
diagnosis of downhole flow conditions. Since in a producing horizontal well
fluid inflowing temperature is not affected by elevational geothermal
temperature changes, the primary temperature differences for each phase (oil,
water, and gas) are caused by frictional effects.
While gas production usually causes a temperature decrease, water entry
results in either warming or cooling of the wellbore. Warmer water entry is a
result of water flow from a warmer aquifer below the producing zone (water
coning). In contrast, produced water can be cooler than produced oil because of
differences in the thermal properties of these fluids. If both oil and water
are produced from the same elevation, oil is heated more by friction while
flowing in a porous medium than water is resulting in the produced water having
a lower inflow temperature than the oil. Water entry by coning is relatively
easy to detect from the temperature profile because of its warmer inflow
temperature, but water breakthrough from the same elevation as the oil may not
be obvious.
In this paper, we illustrate the range of inflow conditions for which
water-or-gas entry locations can be identified from the temperature profile of
a wellfrom measurable temperature changes. Using a numerical
wellbore-temperature-prediction model (Yoshioka et al. 2005a), we calculated
temperature profiles for a wide range of water-inflow conditions.In these
calculations, we assumed that one section of the well produced water or gas,
while the rest of the open section of the well produced oil. From sensitivity
studies, we showed the predictions of the relative water-and-gas production
rates that create detectable temperature anomalies in the temperature profile
along the well. By using the model to match an actual temperature log from a
horizontal well, we demonstrate how this model can be used to identify
water-inflow locations.
Introduction
Temperature logs have been used to locate water entries. Some field examples
(Tolan et al. 2001; Foucault et al. 2004) reported the successful
identification of water entry and prevention of its further production.
However, the identification is often made by intuition. That is, gas entries
reduce the wellbore temperature, and water entries increase the temperature.
The inferences are also qualitative. There is no means to determine the rate of
water entry, for example. To optimize well performance, we need a better method
to identify water or gas entries.
We will analyze anomalous temperature changes along a flowing horizontal
well using a temperature model for horizontal wells. The main difference of the
model from the vertical thermal wellbore models (Hill 1990; Ramey 1962; Sagar
et al. 1991) is that the geothermal temperature is constant along a horizontal
well. Temperature deviations from the geothermal temperature are caused by
changes in flow conditions in the reservoir and wellbore. If we assume that all
the fluids in the wellbore are produced from the same elevation (i.e.,the
temperatures are the same at the boundary), the reservoir energy balance can be
solved as a 1D problem. To infer the temperature behavior with water coning,
the problem needs to be solved in 3D (Dawkrajai et al. 2006). The detailed
discussions of the prediction model are in the following section.
Model Description
We have used two different models in this study. For water produced from the
same elevation as the oil, we consider a segmented reservoir and multiphase
flow in the wellbore. We also consider a steady-state reservoir with constant
fluxes from both sides and no flow at the other boundaries (Fig. 1). For water
coning, a 3D reservoir model is used (Fig. 2). The top and sides of the
rectangular reservoir are sealed, and the pressure below the reservoir (the
aquifer pressure) is constant. In both cases, we assumed fully penetrating
horizontal wellbores.
For nonisothermal flow, we can derive the mass-and-energy balance equations
for the reservoir and wellbore. The solution of the coupled reservoir and
wellbore equations provides the temperature and pressure profiles in the domain
of interest.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
27 February 2006
- Meeting paper published:
12 June 2006
- Revised manuscript received:
4 January 2007
- Manuscript approved:
2 July 2007
- Version of record:
20 November 2007
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