TECHNICAL FIELD

This disclosure relates to wellbore fracturing.

BACKGROUND

In hydrocarbon production, production wellbores are often fractured to increase production rates. Fracturing a wellbore involves pumping high pressure fluid (for example, over 10,000 pounds per square inch) into the wellbore in order to over pressure the wellbore. This overpressure event causes the geologic formation in which the wellbore is formed to exceed a near-wellbore stress and rock strength and result in hydraulic fractures. Sometimes, additives, such as “proppants” are added to the high pressure fluid to “prop” open the fractures.

SUMMARY

This disclosure describes technologies relating to cyclic wellbore fracturing.

An example implementation of the subject matter described within this disclosure is a method with the following features. A wellbore is formed within a rock formation. At least a portion of the wellbore is filled with pressurized fluid. A pressure of the pressurized fluid is cycled between 40% of an expected fracture pressure of the rock formation and 85% of the expected fracture pressure of the rock formation. The rock formation is fractured responsive to the cycling pressure.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes flowing, by a pump, the pressurized fluid until a first target pressure is reached, and after the first target pressure is reached, releasing the pressurized fluid until a second target pressure being less than the first target pressure, is reached.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 50% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure from 40% of the expected fracture pressure of the rock formation to 60% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 60% of the expected fracture pressure of the rock formation.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure from 40% of the expected fracture pressure of the rock formation to 70% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 70% of the expected fracture pressure of the rock formation.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure from 40% of the expected fracture pressure of the rock formation to 80% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 80% of the expected fracture pressure of the rock formation.

Aspects of the example method, which can be combined with the example method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure from 40% of the expected fracture pressure of the rock formation to 85% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 85% of the expected fracture pressure of the rock formation.

An example implementation of the subject matter described within this disclosure is a method of fracturing a wellbore. The method includes the following features. At least a portion of a wellbore, formed within a rock formation, is filled with pressurized fluid. A pressure of the pressurized fluid is cycled such that the pressure does not exceed 85% of an expected fracture pressure of the rock formation. The rock formation is fractured responsive to the cycling pressure.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes flowing, by a pump, the pressurized fluid until a first target pressure is reached, and after the first target pressure is reached, releasing the pressurized fluid until a second target pressure being less than the first target pressure, is reached.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. The pressure is at least 40% of the expected fracture pressure for an entire duration of pressure cycling.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 50% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 60% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 60% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 70% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 70% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 80% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 80% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 85% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 85% of the expected fracture pressure of the rock formation.

An example implementation of the subject matter described within this disclosure is a method of fracturing a rock formation. The method includes the following features. At least a portion of a wellbore, formed within a rock formation, is filled with pressurized fluid. A pressure of the pressurized fluid is cycled such that the pressure is sustained at least at 40% of an expected fracture pressure of the rock formation. The rock formation is fractured responsive to the cycling pressure.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes flowing, by a pump, the pressurized fluid until a first target pressure is reached. After the first target pressure is reached, the pressurized fluid is released until a second target pressure, less than the first target pressure, is reached.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. The pressure does not exceed 85% of the expected fracture pressure for an entire duration of pressure cycling.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 50% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 60% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 60% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 70% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 70% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 80% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 80% of the expected fracture pressure of the rock formation.

Aspects of the example wellbore fracturing method, which can be combined with the example wellbore fracturing method alone or with other aspects, include the following. Cycling the pressure includes increasing the pressure to 85% of the expected fracture pressure of the rock formation, and decreasing the pressure to 40% of the expected fracture pressure of the rock formation from 85% of the expected fracture pressure of the rock formation.

Particular implementations of the subject matter described in this disclosure can be implemented so as to realize one or more of the following advantages. The concepts described herein can allow fracturing at sites with lower horsepower available than would otherwise be necessary to successfully fracture geologic formations within a wellbore. Another advantage of the disclosure is it provides a unique injection technique to introduce hydraulic fractures in the geologic formation without any change or addition of hardware or equipment.

The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

