Completion Selection & Design (Sand Production & Sand Quantification)

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For high porosity reservoirs, or reservoirs in high stress environments, sand production, and the disagregation of the wellbore wall during the life of a well is a major consideration.

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For very weak formations and unconsolidated sands, the wellbore and in situ stresses at the start fo production already exceed the formation strengths and the sand will be produced from initial bean-up. This situation requires sand control from day one, which is the situation in the shallower section of the GoM, Niger delta and other young Tertiary reservoirs which have not undergone significant diagenesis during their burial history.

 

For those reservoir formations which have undergone significant diagenesis and cementation during their history, their strengths may be sufficient to withstand the in situ stresses and wellbore stresses at the start of production, but with depletion, the stresses may exceed the rock strength later in field life.

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The onset of this rock failure during the life of the well is a modified form of wellbore stability, which is addressed using specific geomechanical models to estimate the onset of sand production and the allowable well drawdown pressures to avoid, or minimise, sand production. The analysis of sand production also includes the impact of changes to the lower completion design, such as:

• open hole vs cased and perforated completions,

• selective perforations to delay or eliminate sand production,

• oriented perforations.

These analyses have, in the last decade, also included estimating the volumes of sand expected during the life of the well. This is referred to as sand quantification or sand volume and sand rate estimation.

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For competent reservoirs the number of completions available are numerous, and the role of sand production prediction, and more generally of 'sand management' is to assess the best lower completion option for a well or for a field and to;

• optimise the completion to maximise the oil or gas production while,

• reducing or minimise the sand production and the impact of any sand production.

This involves:

• predicting the onset of sand production,

• estimating the volumes and rates of sand production through the life of the well, then

• assessing the optimum lower completions: open hole, cased and perforated, sand screens, sand control.

This is compared to the expected well inflow for the different lower completions.