In the production of oil and gas, operators are usually faced with undesirable by-products: water and sand (or particulate matter). Bringing these unwanted materials to the surface requires additional energy and cost and reduces the total flow of hydrocarbons to the surface. Once water and sand are brought to the surface, additional energy-intensive processes are required to separate them from the oil and gas. Once separated, properly disposing of unwanted materials also can be challenging and costly. Eliminating, or at least reducing, their production is therefore economically beneficial.

Downhole separators are often used to separate fluids and particulate matter. While these devices are effective, they require a substantial amount of energy. Passive, conductive separation based solely on static weight is a relatively slow process and not practical, as the weight difference of water and oil is approximately 10%. This paper discusses the use of a long angular conduit, or deviated wellbore, to passively create convective forces that enhance the separation. In the deviated section, as the heavier water and sand move to the bottom side of the conduit, the net forces push the heavier water and sand to the bottom, resulting in a convective motion pushing the lighter fluid to the top of the conduit. The weight differences in the produced mixture are amplified by the extended length of the conduit, and the heavier liquids and solids quickly separate from the lighter-weight fluids without any additional energy input as the mixture flows through the deviated section.

Laboratory tests show that convective separation can occur more than 10 times faster than natural static conductive separation. Additionally, the convective separator is capable of effective operation with production flow rates up to 6,000 BOPD with a 6 in. production casing. At higher flow rates, the separation is incomplete because of turbulent mixing, and some unwanted materials could be produced at the surface.

Using this approach, no energy is wasted for producing water, as it can be injected in lower strata after separation. The separated water also can be used for water drive in the formation. Sand, on the other hand, might need to be removed periodically. However, such periodic sand removal can be performed without damaging wellhead equipment.

You can access this article if you purchase or spend a download.