An integrated flow model is developed to simulate the flow into horizontal wells with screens. The model is composed of a multi-segment horizontal well model and a near-wellbore model. The multi-segment horizontal well model predicts the pressure losses in a bounded reservoir. The near-wellbore model simulates the fluid flow through the damaged/collapsed zone around the wellbore, mud-cake, wellbore/screen interface, gravel-packed annulus and screen itself.
Using the model, we investigated the effects of degree of screen damage, non-uniform damage removal, mud cake properties, and blank pipe insertion on horizontal well productivity. We examined and compared the long-term horizontal well performance in terms of rate decline and cumulative production as a function of time.
Background
Horizontal wells with sand control problems may be completed with screens. Screens may be used in a variety of ways; prepacked screens in openholes, standalone all-metal screen-only completion in openholes, screens with openhole gravel packing, and premium screens with blank pipe sections.
Prepacked screens may be preferred because of their lower cost. Historically, prepacked screens are used when there is a good chance of gravel pack failure due to incomplete packing with void pockets. Prepacked screens may effectively minimize the sand production. However, they have smaller inflow area, which may cause productivity decline. Also, prepacked screens are vulnerable to being plugged by drilling mud cake, formation sand and fine particles. Preventing/removing the damage to prepacked screen may be the key to maximizing the well productivity. Screens may be partially or completely plugged. Localized partial plugging creates higher flow velocities at non-plugged screen sections, which in turn may initiate screen erosion. Several experimental studies have been dedicated to characterizing the damage to the screen. In several field applications where the prepacked screens were the preferred completion method, sharp declines in well productivity were reported after relatively short production periods.
Horizontal openholes may also be completed with premium quality, all-metal screens in stand-alone (screen only) mode. Recently, a number of industrial studies focused on evaluating the performance of screen-only completions. When used in a stand-alone mode, the screens providing sand retention and resisting to plugging should be chosen. The permeability of formation sand depositing on the screen may have a significant impact on completion efficiency.
If the annulus between the horizontal openhole and screen is gravel packed then the amount of formation sand production may be reduced significantly, screen plugging may be minimized, and inflow may be more uniformly distributed along the completed segments. However, gravel packing is more complex and expensive. Also, incomplete packing in the annulus may lead to localized high velocity hot spots and screen erosion, which would undermine the use of gravel. In horizontal sections, the transportation of the gravel to formation face and packing efficiency could be the major issues.
If the premium quality screens are used with or without gravel packing, the completion cost is high. However, if blank pipes are inserted between the expensive screen segments then the completion cost may be reduced to a level that is comparable with the cost of prepacked screens. However, when the blank pipe segments are distributed along the horizontal well then the contact area between the wellbore and reservoir is reduced and well productivity is decreased to some degree because of the completion pseudoskin factor.
There have been many studies focusing on the technical issues related to horizontal openhole completions with screens.1–23 For convenience, the previous studies focusing on horizontal wells equipped with screens are divided into two categories; experimental studies/field applications and well productivity models.
