ABSTRACT
The production of formation sand is a problem associated with most
oil deposits in the world. Major Sand production effects affect safety,
well or field economics and continuous production. This has prompted the
continued search for solutions to mitigate sand production in the oil
and gas industry over time. The methodology often employed is through
exclusive sand control or passive sand management. The ability to
predict when a formation will fail and produce sand forms the basis as
to what type of sand management strategy to use (whether downhole sand
control system will be required or a sand management approach). As a
result sand prediction forms the basis for major reservoir development
plan. Variety of models available, their applicability and accuracy can
be confusing and not representative of the production experience. Also,
the concept of sand prediction, control and management is often treated
separately. This study views sand prediction, control and management as
an interdependent concept (Holistic). Review of State of the art sand
prediction, control and management is carried out to proffer better
understanding of the concept of sand production management. The
mechanism of sand production is discussed with highlight of major
parameters influencing sand production. It is identified that sand
prediction forms the basis for reservoir development plan, therefore
effective methodology for sand prediction, control and management is
developed. Stepwise approach to carry out this concept is presented with
flow charts and guidelines. In conclusion the study states the
importance of data accuracy in sand prediction, the use of risk
quantification. Quantifying uncertainties inherent in most predictions
will help deploying the right type of sand management strategy in a
formation.
CHAPTER ONE
PROBLEM FORMULATION
1.1 Introduction
The production of formation sand is a major problem encountered
during the production of oil and gas. Over 70 % of the world’s oil and
gas reserves sit in sand formations where sand production is likely to
become an issue during the life of the well (Osisanya, 2010). Sand
production is typical of tertiary formations (with permeability of 0.5
to 8 Darcy) and older formations as they enter their mature stages of
production due to poor completion and impact of depletion. Areas where
severe sand production problems occur include Nigeria, Trinidad,
Indonesia, Egypt, Venezuela, Malaysia, Canada tar sands and Gulf of
Mexico. The reservoirs in these formations lie between 3,500 ft and
10,000 ft (subsea). Generally, the effects of sand production ranges
from economics and safety hazards to well productivity and therefore has
been an issue of interest to tackle in the petroleum industry. Some of
these effects include erosion of downhole and surface equipment,
pipeline blockage and leakage, formation collapse, damage to
casing/production liner due to formation subsidence, and increased
downtime. These devastating effects lead to more frequent well
intervention and workovers generating additional needs for sand disposal
particularly in offshore and swamp locations. The effects of sand
production are nearly always detrimental to the short and or long term
productivity of the well (William and Joe, 2003). In order to mitigate
problems related to sand production new strategies are being
continuously investigated, from prediction to control and management.
The ability to predict when a reservoir will fail and produce sand is
fundamental to deciding whether to use downhole sand control or what
type of sand control to use (Bellarby, 2009).
Sand production occurs normally as a result of drilling and reservoir
management activities. Sand grains are disengaged from the rock matrix
structure under physical (earth stress) and chemical action. The
mechanism of sand production in terms of sand, volumes and sand
producing patterns in the reservoir is needed to optimally develop a
field. Mechanisms causing sand production are related to the formation
strength, flow stability, viscous drag forces and pressure drop into the
wellbore (Osisanya, 2010). The critical factors leading to
accurate prediction of sand production potential and sand production
are: formation strength, in-situ stress, and production rate. Other
factors are reservoir depth, natural permeability, formation
cementation, compressibility, surface exposed to flow, produced fluid
types and phases, formation characteristics, pressure drawdown and
reservoir pressure. Predicting sand production involves developing
empirical and analytical techniques. Empirical techniques relate sand
production to some single parameter or group of parameters such as
porosity, flow or drawdown analytical techniques relates to rock
stresses. Numerical analytical techniques are also sometimes used. They
are models developed from finite element analysis. The techniques above
use production data, well logs, laboratory testing, acoustic, intrusive
sand monitoring devices, and analogy (Osisanya, 2010). At present,
predicting whether a formation will or will not produce sand is not an
exact science and needs more improvement.