Perpustakaan Digital ITB

Area X field Y consists of six stacked sands which are called sand A, B, C, D, E and F. Sand A is still not developed yet because of economic and safety reason. Sand A and B are divided into five flow units/layers and C three flow units. These flow units were injected and produced commingle. All sands except sand A were produced through long open hole completion in producer wells, and steam injected through tubing or casing string which is perforated at all interested zone and injected commingle. Each layer in individual sands has different reservoir characteristic like permeability and thickness. This condition make steam placement into each flow unit (profile control) become very challenging in this field. Darcy Law states that amount of flow through porous media are function of permeability, pressure difference, fluid viscosity and distance. The same thing happens in multi-sand injection which using only perforated tubing and casing string. Steam will tend to flow to layer which has lowest flow restriction. From rock properties stand point, flow will tend to flow to highest permeability or clean sand layer. This condition will cause amount of steam flow to lowest restriction layer will be excessive, on the other hand layers or flow units which relatively have higher flow restriction will suffer and remains cold. Excessive flow to lowest flow restriction layer will cause that layer gets breakthrough first. Once that layer gets breakthrough, steam injection condition will be worse because flow restriction in the breakthrough layers will decrease because steam has formed flow path. This kind of injection condition will cause lower steam usage efficiency because steam is circulated through breakthrough layer, and of course lifting cost will be high because the major operating cost of steam flood is come from steam cost. At the same time flow units or layer which relatively have higher flow restriction do not have enough steam and remain cold, because breakthrough layer has act as a thief zone. As consequence oil at those layers will not be recovered. Usage of critical flow principle will be studied to improve vertical distribution of steam, especially usage of critical flow principle through divergent nozzle. Theoretically, under critical flow condition, downstream pressure will not affect amount of flow through limited entry hole and divergent nozzle. Amount of flow only depends on upstream pressure and other parameters. Usage of divergent nozzle in critical flow will allow rate controlling to each layer which have different reservoir characteristics and injected simultaneously. This method expected can put steam to all layer, so all layer can be heat up and processed simultaneously. Of course, heating up all layers will increase vertical steam sweep efficiency which finally increases oil recovery.