96
The Chemistry and Technology of Petroleum
The main consideration regarding well spacing is sand continuity, whose determination may
require the combined interpretation of geologists, stratigraphers, and logging and petrophysical
experts. Sand continuity is vital in the selection of well spacing for processes involving interwell
fluid displacement. Partial communication in sands where only a fraction of the interval correlates between well locations invariably leads to poor recoveries and poor effective transmissivity.
Knowledge of the depositional setting of the sands may be crucial in establishing whether open
intervals in nearby wells are part of the same blanket sand or are likely to be in unconnected and
meandering river channels. Regional trends in the direction of river channels may result in an apparent anisotropy in reservoir permeability, with relatively good communication between wells in the
same channels and poor or no communication in a transverse direction.
Displacement processes are not indicated where communication is poor over relatively short
distances. Instead, cyclic steam injection or some other stimulation treatment that does not depend
on interwell communication is preferred.
Another factor related to well spacing is the well pattern. Because of the extensive use of repeated
well patterns (such as five-spots) in waterflooding, they were considered necessary in the early years
of thermal recovery. Now, however, the use of repeated regular well patterns is not always essential
for the success of field projects. The choice of well locations is important in reservoirs having significant dip or a strong lateral aquifer influx.
In addition to the factors already discussed, there are a few other important considerations in
selecting a reservoir for thermal projects. Foremost are any factors that may affect the control of the
operation, especially where safety is involved.
Control means that the fluids are injected only into the target reservoir and that both displaced
and injected fluids are collected efficiently and safely. The leakage of produced or injected fluids to
the surface is an extreme example of loss of control.
Conditions that should be considered and evaluated carefully are injection pressures close to the
fracture initiation pressure or close to the estimated pressure limits of well equipment (especially in
old wells) and reservoirs where communication with nearby outcrops is likely. These could lead to
fluid contamination of overlying formations, loss of production, pressure, and control, and possibly
both unexpected workover costs and early termination of the project.
Where displaced oil can bypass a producing well, it is generally desirable on technical grounds
(but not necessarily justifiable economically) to fracture the well and to maintain it in unimpaired
condition, especially where low-flow-resistance zones near the well compete for the flow of oil.
Stimulation of producers by cyclic steam injection has long been recognized as an excellent method
for reducing the resistance to flow into these wells. Special attention should be paid to methods for
avoiding or minimizing the resaturation of previously depleted zones or the saturation of previously
clean sands (such as zones below a water/oil contact).
REFERENCES
Ancheyta, J. and Speight, J.G. 2007. Hydroprocessing of Heavy Oils and Residua. CRC Press, Taylor & Francis
Group, Boca Raton, FL.
Andersen, S. I. and Speight, J. G. 1999. Thermodynamic models for asphaltene solubility and precipitation.
Journal of Petroleum Science and Engineering, 22: 53.
Anderson, W. G. 1986. Wettability literature survey: Part 1. Rock-oil-brine interactions and the effects of core
handling on wettability. Journal of Petroleum Technology, October: 1125–1144.
API. 2003. Sampling petroleum reservoir fluids. Report API RP 44, American Petroleum Institute, Washington,
DC, 1 April 2003.
ASTM D128. 2012. Standard Test Methods for Analysis of Lubricating Grease. Annual Book of Standards.
American Society for Testing and Materials, West Conshohocken, PA.
ASTM D2006. 2012. Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils
by the Precipitation Method (Withdrawn 1975). Annual Book of Standards. American Society for Testing
and Materials, West Conshohocken, PA.
The Chemistry and Technology of Petroleum
The main consideration regarding well spacing is sand continuity, whose determination may
require the combined interpretation of geologists, stratigraphers, and logging and petrophysical
experts. Sand continuity is vital in the selection of well spacing for processes involving interwell
fluid displacement. Partial communication in sands where only a fraction of the interval correlates between well locations invariably leads to poor recoveries and poor effective transmissivity.
Knowledge of the depositional setting of the sands may be crucial in establishing whether open
intervals in nearby wells are part of the same blanket sand or are likely to be in unconnected and
meandering river channels. Regional trends in the direction of river channels may result in an apparent anisotropy in reservoir permeability, with relatively good communication between wells in the
same channels and poor or no communication in a transverse direction.
Displacement processes are not indicated where communication is poor over relatively short
distances. Instead, cyclic steam injection or some other stimulation treatment that does not depend
on interwell communication is preferred.
Another factor related to well spacing is the well pattern. Because of the extensive use of repeated
well patterns (such as five-spots) in waterflooding, they were considered necessary in the early years
of thermal recovery. Now, however, the use of repeated regular well patterns is not always essential
for the success of field projects. The choice of well locations is important in reservoirs having significant dip or a strong lateral aquifer influx.
In addition to the factors already discussed, there are a few other important considerations in
selecting a reservoir for thermal projects. Foremost are any factors that may affect the control of the
operation, especially where safety is involved.
Control means that the fluids are injected only into the target reservoir and that both displaced
and injected fluids are collected efficiently and safely. The leakage of produced or injected fluids to
the surface is an extreme example of loss of control.
Conditions that should be considered and evaluated carefully are injection pressures close to the
fracture initiation pressure or close to the estimated pressure limits of well equipment (especially in
old wells) and reservoirs where communication with nearby outcrops is likely. These could lead to
fluid contamination of overlying formations, loss of production, pressure, and control, and possibly
both unexpected workover costs and early termination of the project.
Where displaced oil can bypass a producing well, it is generally desirable on technical grounds
(but not necessarily justifiable economically) to fracture the well and to maintain it in unimpaired
condition, especially where low-flow-resistance zones near the well compete for the flow of oil.
Stimulation of producers by cyclic steam injection has long been recognized as an excellent method
for reducing the resistance to flow into these wells. Special attention should be paid to methods for
avoiding or minimizing the resaturation of previously depleted zones or the saturation of previously
clean sands (such as zones below a water/oil contact).
REFERENCES
Ancheyta, J. and Speight, J.G. 2007. Hydroprocessing of Heavy Oils and Residua. CRC Press, Taylor & Francis
Group, Boca Raton, FL.
Andersen, S. I. and Speight, J. G. 1999. Thermodynamic models for asphaltene solubility and precipitation.
Journal of Petroleum Science and Engineering, 22: 53.
Anderson, W. G. 1986. Wettability literature survey: Part 1. Rock-oil-brine interactions and the effects of core
handling on wettability. Journal of Petroleum Technology, October: 1125–1144.
API. 2003. Sampling petroleum reservoir fluids. Report API RP 44, American Petroleum Institute, Washington,
DC, 1 April 2003.
ASTM D128. 2012. Standard Test Methods for Analysis of Lubricating Grease. Annual Book of Standards.
American Society for Testing and Materials, West Conshohocken, PA.
ASTM D2006. 2012. Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils
by the Precipitation Method (Withdrawn 1975). Annual Book of Standards. American Society for Testing
and Materials, West Conshohocken, PA.