The research is aimed at the understanding of the various diagnostic
plots for the analysis of water production that are available as well as
the application of these methods in a case study. It also aimed at the
establishment of a work flow for the evaluation of water production
mechanisms. A workflow was developed that combines numerical simulation
and diagnostic plots to analyze the water production performance in a
reservoir. This workflow was validated using a case study.
The multi-layer reservoir model with varying vertical permeability
was constructed using a numerical simulator with the reservoir
properties of the case study. Trends from the field data were analyzed
using the trends observed from the simulated data as templates.
For the production wells, oil rate and water rate versus time plots
as well as the X-plot were used to evaluate water production
characteristics of the case study. The water-oil ratio (WOR), WOR
derivative and X-Plot were used for the field production diagnosis while
the Hall and the Hearn Plots were used for the water injection well
diagnosis. The results of the diagnostic plots showed that multi-layered
channelling was the controlling mechanism and the cause of the water
production in the case study. For the injection wells, the plots
indicated that some wells in the case study had the problem of extensive
near wellbore fracturing while other wells had the problem of wellbore
The workflow and results of this study can be applied by reservoir
and production engineering teams to other reservoirs to diagnose water
production mechanisms; identify sources of water production, and provide
information for planning water management programmes to mitigate
excessive water production problems.
1.1 DESCRIPTION OF PROBLEM
Produced water is any water that is present in a reservoir with the
hydrocarbon resource and is produced to the surface with the crude oil
or natural gas. This water could either come from an aquifer or from
injection wells in water flooding process. The production of this water
alongside the oil from any reservoir is a condition that is natural in
all reservoirs. It is expected that water production would increase with
the life of the reservoir. However, a premature increase in the
production of water in any reservoir is an undesirable condition. Excess
or premature water production, exists with associated cost implication
on the surface facilities, artificial lift systems, corrosion and scale
problems. Another effect that ensues is a decrease in the recovery
factors as oil is left behind the displacement front, thereby reducing
the performance of the reservoir. All these along with the decrease in
the quantity and quality of the oil imply a reduced profitability.
Globally, as at 2002, analysis showed that three barrels of water is
produced to one barrel of oil and the cost of water handling ranges from
5 to 50 cents, where this cost is a function of the water cut (Bailey
et al, 2000). It is therefore imperative that actions be taken to reduce
this adverse effect, as this will not just lead to potential savings
but its greatest values comes from potential increase in oil production
and recovery. To control the produced water effectively, the source or
the mechanism of the water problem must be identified. Diagnostic plots
have been used successfully to identify the mechanism of water
production and that is the focus of this work.
1.2 STUDY OBJECTIVES
Reservoir simulation would most likely describe a reservoir
adequately but a quicker and cheaper way to analyse the performance of a
reservoir is by the use of analytical and diagnostic plots, therefore,
this research work is aimed at:
· Developing a work flow for the evaluation of water production mechanisms.
· Presenting the workflow by considering detailed step by
step approach on how water production problems in the reservoir can be
diagnosed to support water management planning for mitigation actions.
· The use of a couple of case studies to demonstrate the
application of the workflow and diagnostic plots to identify water
· Formulating guidelines on how to mitigate water production and thereby optimizing well performance and oil recovery.