Method for sand control in oil, gas and water wells

Wells – Processes – Cementing – plugging or consolidating

Reexamination Certificate

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C166S288000, C166S300000, C166S401000

Reexamination Certificate

active

06364019

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved method for sand control in oil, gas and water wells and more particularly to a method for treating subterranean sand formations adjacent to a bore hole. The treatment is for the purpose of forming a permeable solid barrier which restrains the movement of sand particles while maintaining the permeability of the formations.
BACKGROUND FOR THE INVENTION
Production of oil, gas and water from unconsolidated or weakly consolidated formations is normally accompanied by the production of formation sand particles along with the produced fluids. The production of sand with the well fluids poses serious problems such as the erosion of sub-surface and surface production facilities and the accumulation of the sand in the wellbore and surface separators. Several methods such as gravel packing, screens and plastic consolidation have been in use for many years with varying success. However, these methods have several-technical and cost limitations.
Other method s for treating subterranean sand formations which are adjacent bore holes are disclosed in the Canadian Patent No. 700,740 of Marx, and in the U.S. Pat. No. 3,172,468 of Watson et al., U.S. Pat. No. 3,182,722 of Reed, U.S. Pat. No. 3,217,800 of Smith, U.S. Pat. No. 3,388,743 of Engle et al. and U.S. Pat. No. 3,974,877 of Redford. The methods disclosed therein consolidate incompetent formations by in-situ oxidation of heavy crude oil. Such methods are applicable to formations containing bitumen or heavy crude oil and utilize in-situ combustion involving high temperatures.
A Canadian patent No. 713,989 of Goodwin et al. discloses a method for consolidating heavy oil formations by oxidation of the heavy oil at a temperature of between 350 and 500° F. Another Canadian patent No. 1,266,429 of Hanna discloses a method of treating an unconsolidated formation by heating heavy crude oil above ground level. The heated crude oil is then injected into the bore hole to heat the unconsolidated formation adjacent the bore hole to a temperature of between 35°-135° C. (95° F.-275° F.). The elevated temperature supports the low temperature oxidation of the oil contained within the formation. Unheated oxygen containing gas is then injected into the bore hole and into contact with the heated formation to precipitate asphaltenes.
Another method for treating incompetent sand formations is disclosed in U.S. Pat. No. 3,910,351. As disclosed therein, a cavity is formed around a bore hole and 10-80 mesh sand introduced into the cavity. This step is then followed by the injection of bituminous petroleum. An asphalt-precipitating solvent is then injected followed by the injection of a heating fluid to solidify the precipitated asphalt.
In general, the previously mentioned processes use heavy crude oil that are either naturally present in the formation or heated and injected into the formation. In such cases, the oxidation temperature is higher than the formation temperature. Therefore, the processes are applicable to formations that are treated by the in-situ combustion process or in processes which involve extensive heating of the formation, crude oil and air with temperatures higher than the formation temperature. Furthermore, the use of heavy crude oil normally results in a significant loss of permeability and a reduced well productivity.
Accordingly, a prime object of the present invention is to develop a consolidating method using in-situ low-temperature oxidation (LTO) of a hydrocarbon material. This low temperature oxidation is obtained at a temperature close to the formation temperature and produces consolidated sand with a minimum loss of permeability and high compressive strength. This allows the maximum production of oil, gas or water without sand production. Further, the resulting consolidated sand is stable against the flow of formation fluids and other well-treatment fluids such as acids.
Several factors influence the low temperature oxidation process. For example there are the type of hydrocarbon material being oxidized, the oxidation temperature, the oxidation duration, the presence of catalytic materials (such as clay) in the sand and the sand grain size. The effect of these factors on the process can be expressed in terms of the degree of consolidation obtained as measured by the compressive strength of the consolidated sand, the retention of permeability and the stability against formation and treatment fluids.
BRIEF SUMMARY OF THE INVENTION
In essence, the present invention contemplates an improved method for treating subterranean incompetent sand formations adjacent to a well or bore hole. This method or treatment is for the purpose of forming a permeable barrier which restrains the movement of sand particles and at the same time retains a high degree of permeability. The method includes the step of forming a consolidation fluid containing an asphaltene or preferably asphalt and a hydrocarbon solvent such as naphtha, reformate, or other aromatic solvent with a concentration of at least about 40 grams of asphaltene per 100 ml of solvent. In the preferred embodiments of the invention, the concentration of asphalt ranges from about 40 grams to about 80 grams of asphalt per 100 ml of solvent.
The consolidation fluid is then injected into the sand formation to saturate the sand in a zone around the bore hole. For example, the consolidation fluid is injected to saturate the sand for a radial distance of from about 1 to about 2 feet. This saturation step displaces any natural oils or water in the sand formation.
After injecting the consolidation fluid into the sand, an oxygen containing gas such as air is injected into the sand formation. This oxygen containing gas is injected at a temperature of about 100° C. to about 150° C. and preferably at a temperature of about 100° C. The gas injection is continued for a period of time which is sufficient to solidify a thin film of asphaltene on the surface of the sand particles.
In a preferred embodiment of the invention, the method for treating subterranean incompetent sand formation includes the step of monitoring the oxygen content of an effluent gas until the oxygen concentration of the effluent gas is essentially the same as the oxygen concentration of the injected gas. When the oxygen content of the effluent gas is approximately equal to the oxygen content of the injected gas, the injection is stopped and the treatment has been completed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention relates to the in-situ consolidation of incompetent sand formations containing crude oil (heavy or light), gas or water. The incompetent sand is consolidated by means of low-temperature oxidation (LTO) of a hydrocarbon material that is either naturally present in or injected into the formation. This treatment creates a consolidated sand matrix around the well bore that has high compressive strength, minimum loss of permeability and stability against formation and well treatment fluids.
Several factors influence the low temperature oxidation process. For this reason, an experimental program was developed. That program will be described with reference to a number of examples. Such examples incorporated small sand packs, 2″ diameter by 4″ long and 1″ diameter by 2.5″ long. Different sand grain sizes representing different actual formations were tested. The oxidation was then conducted using different hydrocarbon material compositions, different oxidation temperatures, oxidation duration, different oxygen partial pressure and with and without the presence of catalytic materials in the sand packs. After determining the preferred oxidation (consolidation) conditions, consolidation tests were conducted on a full scale wellbore model resembling commercial wells to test the feasibility of field application of the process. These tests will be described hereinafter.
In one embodiment of the invention, an unconsolidated sand containing crude oil, gas or water was penetrated by a well bore. The unconsolidated sand was

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