RU2447282C2 - Method to detect hydrocarbon-containing beds in process of their opening with drilling - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method to detect hydrocarbon-containing beds in process of their opening with drilling includes pumping of an indicator fluid with radon into a pore volume of permeable beds in the area with thickness of 0.03-0.05 m from the well wall deep into the bed, for at least three times. Gamma-ray logging is carried out. The indicator fluid is displaced along the well bore, by pumping of 0.1 m³ of bore fluid from the wellhead to maintain initial concentration of radon in the indicator fluid. The given mathematical expression is used to judge on availability of hydrocarbon-containing beds.

EFFECT: improved accuracy of detection of promising hydrocarbon-containing beds in the open bore of the well after their opening.

Description

The invention relates to geophysical methods for researching wells, in particular to the identification of hydrocarbon-containing formations in drilled, production and other purposes wells.

It is known that during the opening of reservoir formations, the main factors that distort the properties of the formation in the near-wellbore zone are the active and deep displacement of the formation fluid deeper into the formation from the borehole wall and the mudding of its pore space by filtration products.

Since a long period of time elapses between the moment the collector is opened and its investigation, distorting factors change the initial permeability and composition of the fluid saturating fluid so much that it becomes almost impossible to establish them using traditional methods of electrical, acoustic, thermometric and radiometric logging.

Hydrodynamic methods, due to the complexity of determining the initial permeability and fluid saturation, it is impossible to bind these parameters to a specific reservoir, since they give integral characteristics of the parameters of interest.

The known method of radioactive indicators for determining permeable formations in the near-borehole space of a drilled well, for assessing their filtration-capacitive properties and the nature of saturation, described in the book by Filippov V.P. The use of the indicator method for radon. - M.: VNIIOENG OJSC. - 2003. - 272 s., Which consists in the fact that the drilling fluid is injected with radon into the wellbore through the drill pipe into the test interval after drilling, after opening the test interval and conducting control logging, in order to determine the permeable formations.

After the formation, by means of tripping and lifting operations, of the zone of indicator penetration into the reservoirs, the replacement of a portion of the radioactive indicator fluid with non-radioactive when flushing the well, repeated gamma-ray logging is performed. By analyzing gamma-ray logs, reservoirs are separated according to reservoir properties and saturation according to the dependence graph J _p / J _p (m), where J _p is the gamma radiation intensity of the formation with radon without background, J _p is the gamma radiation in the wellbore against the formation after injection of radon, m is the porosity of the formation.

The disadvantage of this method is that it is impossible to assess the saturation nature of the selected formations, since during the round-trip operations of the drill string it is not possible to achieve the required depth of penetration of the indicator fluid into the reservoirs due to small values in absolute value and duration of the developed pressure, as well as alternating the nature of the impact (after the descent of the column follows its rise).

Due to these reasons, radon from the filtrate penetrated into the formation does not have time to redistribute into the hydrocarbon phase of the porous space of the reservoir.

A single increase in pressure to form the zone of penetration of the indicator into the reservoirs, as proposed in the book, will also not allow the separation of hydrocarbon-containing formations, since this technology does not aim at the most complete transition of radon from the filtrate to the hydrocarbon phase.

The closest is the patent No. 2375569, "A method for detecting carbohydrate-bearing strata", authors: V. Kilyakov. and etc.

This method is used when drilling prospective horizons.

The main objective of the method is the allocation of hydrocarbon-containing formations in the process of drilling a well.

This is achieved by activating the indicator fluid with radon. At the end of the sinking, after the drill string is lifted, gamma-ray logging is carried out and hydrocarbon-containing formations are isolated by gamma-radiation intensity values.

The disadvantage of this method is that it is not applicable in cased perforated wells, as well as in intervals whose permeability is distorted by mudding.

The technical result, to which the claimed invention is directed, is to increase the reliability of identifying promising hydrocarbon-containing formations in an open wellbore after opening them.

This is achieved due to the multiple injection of indicator fluid with radon through the pore space of permeable formations in an area 0.03-0.05 m thick from the borehole wall into the formation.

Using the proposed method will allow us to distinguish hydrocarbon-containing formations in extended open intervals of the study (200-300 m) a long time after their penetration, as well as in perforated cased intervals of unconserved wells, i.e. in those formations where it is impossible to create a deep penetration of the indicator fluid into the reservoir by existing methods.

To achieve the named technical result in the proposed method, including gamma-ray logging, injection of indicator fluid with radon into the pore space of the formations, and the injection of indicator fluid with radon into the pore space of the permeable formations in an area 0.03-0.05 m thick from the well wall into the formation is carried out at least three times, is carried out gamma ray, the indicator fluid is displaced through the borehole by pumping from the mouth of 0.1 m ³ of mud to maintain the original concentration of radon in the indicator second fluid and the presence of hydrocarbon reservoirs is judged by the function J _n / J _p (m), where:

J _p - the intensity of gamma radiation of the formation with radon without background;

J _{p - the} intensity of gamma radiation in the wellbore against the formation after injection of radon;

m is the porosity of the reservoir.

The method includes conducting gamma-ray logging, injection into the interval of the studied formations of the indicator fluid with radon, tripping of the drill string to form a zone of penetration into the pore space of the formation of indicator fluid with radon, periodically creating pressure at the wellhead, keeping the well under pressure, slow pressure reduction, flushing the test area from the indicator, conducting gamma-ray logging after each operation.

In the process of drilling, after stopping the well for research in the studied interval of the open wellbore, the background gamma-ray logging is measured. The isotope is injected with the help of a cementing unit into the calculated volume of indicator fluid to study an extended interval (200-300 m) of an open wellbore. Through the drill pipe string, this volume of labeled indicator fluid is pumped into the test interval and the formation of the penetration zone of the indicator fluid is performed by round-trip operations of the drill string followed by alternating stepwise pressure increase at the wellhead and its slow decrease (at least three times). To achieve passage through the pore space of the formation in an area 0.03-0.05 m thick from the well wall, the indicator fluid is displaced along the wellbore by injecting 0.1 m ^{3 of} drilling fluid from the wellhead to maintain the initial radon concentration in the indicator fluid against the hydrocarbon reservoir. The results of each open-hole operation are controlled by gamma-ray logging. The presence of hydrocarbon-containing formations is judged by the dependence of J _p / J _p (m), where:

J _p - the intensity of gamma radiation of the formation with radon without background;

J _p - the intensity of gamma radiation in the wellbore against the formation after injection of radon;

m is the porosity of the reservoir.

Claims (1)

A method for identifying hydrocarbon-containing formations during drilling by gamma-ray logging, injection of indicator fluid with radon into the pore space of the formations, characterized in that the injection of indicator fluid with radon into the pore space of the permeable formations in an area of 0.03-0.05 thickness m from the wellbore wall into the interior of the reservoir is performed at least three times, is carried out gamma ray, the indicator fluid is displaced through the borehole by pumping from the mouth of 0.1 m ³ of mud to maintain the initial concentration and radon in the indicator fluid and the presence of hydrocarbon-bearing strata are judged on the dependence
J _p / J _p (m),
where J _p - the intensity of gamma radiation of the formation with radon without background;
J _p - the intensity of gamma radiation in the wellbore against the formation after injection of radon;
m is the porosity of the reservoir.