Apparatus and methods for separating sand from well fracturing return water

Apparatus and methods for removing sand or other particulate from well fracturing return water are disclosed. In a sand separator box, a barrier element divides the tank into an upper compartment and a lower compartment. Particulate-laden return water flows through a gas separator and then into the upper compartment of the box. The barrier element allows the water in the upper compartment to pass into the lower compartment while keeping the sand or particulate in the upper compartment. As water accumulates in the lower compartment, it is pumped out to storage tanks or back to the well for reuse.

BACKGROUND OF THE INVENTION

The field of the invention is oil and gas well equipment. In oil and gas wells, sand or similar particulate material is often mixed with water and injected into the well under high pressure. The pressurized liquid helps to fracture underground formations around the well bore. This allows oil and/or gas in the underground formations to flow more freely to the well bore. The fracturing is achieved hydraulically via pumping the liquid into the well under high pressure. The sand acts a proppant to hold the underground fractures open after the water is removed.

As pressure on the well bore is released, the injected water returns back up and out of the well. For environmental and other reasons, the return water is captured and held in a holding reservoir or tank. The return water may then be reused in the fracturing process. The return water however typically contains a substantial amount of sand. The sand must be separated from the water. Various so-called sand trap or de-sanding apparatus have been developed for this purpose. However, these existing designs have various disadvantages in performance, efficiency, utility, cost or other factors. Accordingly, an improved sand separator is needed.

SUMMARY OF THE INVENTION

Novel apparatus and methods for removing sand or other particulate from return water have now been invented. In a first aspect of the invention, well equipment, includes a barrier element in a tank substantially dividing the tank into an upper compartment and a lower compartment. A gas separator is associated with the tank, with sand or particulate-laden water outflow from the gas separator moving into the upper compartment of the tank. The barrier element allows the water in the upper compartment to pass into the lower compartment while keeping the sand or particulate in the upper compartment.

Other objects, features and advantages will become apparent from the following detailed description.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now in detail to the drawings, and specifically toFIGS. 1-3, a new separator20for use in well operations has a tank or box50, which may be provided as a roll-off box. The separator20can then be readily moved to a well site via a roll-off truck. As shown inFIGS. 2 and 3, a particle barrier56divides the interior space of the tank50into an upper compartment62and a lower compartment58. The particle barrier56may be a filter material or liner, a screen, or other element that will allow water, but not particles, to pass through it. For well operations, the particles are typically sand particles, as further described below.

A particle barrier support54may be used to support the particle barrier56. For example, where a non-structural material, such as filter material, mesh, or screen is used as the particle barrier, a metal (e.g., steel) support may be provided to support the particle barrier. As one example, as shown inFIGS. 2 and 3, a steel support54is supported on bars within the tank50. In this case, the support54may be perforated or punched steel sheet, formed into a five-sided box within the tank50. One or more fold down walkways80may be provided on the outside of the tank50, to provide easy access for installing, operating and maintaining the separator20, and for collecting samples of material from the tank50.

FIG. 7shows an example of the use of the separator20. In this example, at the well site10, the return water18from the well head12flows under return pressure through return pipelines70, optionally through a manifold16, to one or more separators20. Referring now toFIGS. 2-5, the return water18enters into a gas separator22, also known as a gas buster, which may be positioned on, or permanently attached to, a top surface or cover74of the tank50of the separator20. The gas separator22separates well gas, typically natural gas, from the return water18flowing through the gas separator22. The gas may then be vented to the atmosphere through an exhaust82. The return water18flows out of the gas separator and into the tank50. The gas separator22may be attached as an integral part of the tank50of the separator20. The tank50may have solid rolling lids52which can be opened during operation of the separator20, to allow the return water to flow out of the gas separator22and into the tank. The solid rolling lids52may be closed during transport of the separator20, to prevent release of sand from the tank50, as is required by Department of Transportation laws.

FIG. 7shows use of two separators20and a manifold16. When one separator is filled from ongoing use, it may be disconnected, picked up by the roll-off truck42, and moved to a disposal site where the contents of the separator20may be emptied. During this time, the second separator20continues to operate. As a result, there is no interruption in handling of return water from the well. Well operations therefore can continue uninterrupted. The manifold16may optionally be set up to route return water to two, three, four or more separators20, depending on the volume of return water to be handled and other factors. Valves and disconnect fittings may be used in the pipelines shown inFIG. 7, as is well known in the field.

The return water18contains entrained particles, such as sand particles, which are preferably separated out from the water. This occurs within the tank50. Referring still toFIGS. 2-5, after degasification, the return water18flows or drains out of the gas separator22via outlets66and moves into the upper compartment62of the tank50. From the upper compartment62, water moves through the barrier56into the lower compartment58. Particles in the water are blocked by the barrier56and remain in the upper compartment62. As shown inFIG. 3, the particles, such as sand64, accumulate on top of the barrier56. As additional return water18moves into the tank50, water (largely free of particles) accumulates in the lower compartment58and particles accumulate in the upper compartment62.

Referring once again toFIG. 7, to maintain the particle separating operation, the water level in the tank should remain below the barrier56, by pumping water out of the lower compartment58via pipelines72. One option is to pump water from the lower compartment back via a second pump pipeline78to the well head for reuse, via a reverse pump14and a reverse pipeline84. Water from the lower compartment58may in addition, or alternatively, be pumped out through a transfer pipeline25to one or more holding tanks, such as the frac tanks30. InFIG. 7, a transfer pump24driven by a generator26on a pump/generator trailer28is used for this purpose. Water may be stored in the frac tanks30until it is withdrawn via a manifold32and reused in the well via a first pump pipeline76, the reverse pump14, and the reverse pipeline84.

Thus, novel apparatus and methods have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.