Page 263 - Introduction to Petroleum Engineering

250 PRODUCTION PERFORMANCE
depositional model. The reservoir framework and structure should be consistent.
Flow tests on cores give information about permeability. Well logs are a primary
source of information about net pay, fluid contacts, porosity, and water saturation. In
some cases, data from different scales provide information about the same feature.
Data from multiple sources must be consistent from one source to another.
For example, well log and seismic data provide information about the depths of
fluid contacts. If there is a difference between the two sources of data, they must be
reconciled. Similarly, differences between permeability from flow tests in cores and
permeability from transient well tests may have to be reconciled.
Field performance data is acquired from a variety of sources. Seismic data is
acquired from seismic surveys by geophysicists. Well logs are typically acquired and
analyzed by geoscientists and engineers. The database should include well pressure
measurements and data characterizing the performance of surface and subsurface
equipment. Subsurface equipment includes casing, tubing, subsea templates, and
electric submersible pumps (ESPs). Surface equipment includes well heads, flow
lines, separators, compressors, and other facilities like offshore platforms.
Data needs to be trustworthy. In some cases it is possible to ascertain the uncer-
tainty associated with data. For example, multiple measurements of properties such
as porosity and permeability can be used to conduct a statistical analysis if the data
is available. It is a significant challenge to maintain a complete, up‐to‐date, and accu-
rate database.

Example 13.1 Well PI and Workover Analysis

A. Suppose a well originally produces 10 000 STBO/day at a pressure draw-
down of 10 psia. What is the well PI?
B. The well PI declined 5% a year for the first 2 years of production. What is
the well PI at the end of year 2?
C. The well PI at the beginning of year 3 is 750 STBO/day/psia. A well test
showed an increase in skin and the skin is positive. Does the well need a
workover?
Answer
10000 STBO/day STBO/day
A. PI 1000
10 psia psia
STBO/day STBO/day
.
.
.
B. 1000 10 05 10 05 902 5
psia psia
C. Yes. S > 0 implies that well stimulation could improve flow.

13.1.1 Bubble Mapping
Bubble mapping can be applied to spatially distributed variables such as flow rates,
reservoir pressures, fluid and rock properties, and cumulative production. It is a
procedure that provides a visual comparison of spatially distributed variables in an