Summary
Fluid properties descriptions are required for the design and implementation
of petroleum production processes. Increasing numbers of deep water and subsea
production systems and high-temperature/high-pressure (HTHP) reservoir fluids
have elevated the importance of fluid properties in which well-count and
initial rate estimates are quite crucial for development decisions. Similar to
rock properties, fluid properties can vary significantly both aerially and
vertically even within well-connected reservoirs.
In this paper, we have studied the effects of gravitational fluid
segregation using experimental data available for five live-oil and condensate
systems (at pressures between 6,000 and 9,000 psi and temperatures from 68 to
200°F) considering the impact of fluid composition and phase behavior. Under
isothermal conditions and in the absence of recharge, gravitational segregation
will dominate. However, gravitational effects are not always significant for
practical purposes. Since the predictive modeling of gravitational grading is
sensitive to characterization methodology (i.e., how component properties are
assigned and adjusted to match the available data and component grouping) for
some reservoir-fluid systems, experimental data from a specially designed
centrifuge system and analysis of such data are essential for calibration and
quantification of these forces. Generally, we expect a higher degree of
gravitational grading for volatile and/or near-saturated reservoir-fluid
systems.
Numerical studies were performed using a calibrated equation-of-state (EOS)
description on the basis of fluid samples taken at selected points from each
reservoir. Comparisons of measured data and calibrated model show that the EOS
model qualitatively and, in many cases, quantitatively described the observed
equilibrium fluid grading behavior of the fluids tested. First, equipment was
calibrated using synthetic fluid systems as shown in Ratulowski et al. (2003).
Then real reservoir fluids were used ranging from black oils to condensates
[properties ranging from 27°API and 1,000 scf/stb gas/oil ratio (GOR) to 57°API
and 27,000 scf/stb GOR]. Diagnostic plots on the basis of bulk fluid properties
for reservoir fluid equilibrium grading tendencies have been constructed on the
basis of interpreted results, and sensitivities to model parameters estimated.
The use of centrifuge data was investigated as an additional fluid
characterization tool (in addition to composition and bulk phase behavior
properties) to construct more realistic reservoir fluid models for graded
reservoirs (or reservoirs with high grading potential) have also been
investigated.
© 2009. Society of Petroleum Engineers
View full textPDF
(
529 KB
)
History
- Original manuscript received:
7 July 2008
- Meeting paper published:
21 September 2008
- Revised manuscript received:
4 December 2008
- Manuscript approved:
7 December 2008
- Published online:
3 September 2009
- Version of record:
28 October 2009
View Cart
