PRACTICAL APPROACH TO EFFECTIVE SAND PREDICTION, CONTROL AND MANAGEMENT
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.