Method for determination of oil-filled formations

FIELD: oil and gas industry.

SUBSTANCE: bore core is selected and examined, induction logging and induced gamma-ray logging or neutron-neutron logging is made and log curves are analysed for the roof of production tier. At that formations with apparent resistivity are identified with values less than 6-8 Ohm/m during induction logging and against values at curves of induced gamma-ray logging or neutron-neutron logging making less 85% and less than values of lower formations. Among these formations it is necessary to select strata without loamy lintels and strata of carbonate oil-filled formations and values of apparent resistivity not less than 15 Ohm/m against data of induction logging. Then sedimentary types for the selected formations is defined and if oil-saturated sandstone is present then conclusion is made about terrigenous origin of these formations. Then values are specified for porosity coefficient, permeability and oil-saturation coefficients and when lower limits for this region are exceeded the indentified formations will be referred to productive formations.

EFFECT: increase of operational efficiency during installation of the bottom-hole complex, improvement of level of detail and authenticity of GIS data for identification of geological rating for rock masses.

1 tbl

 

The invention relates to the oil industry and can find application in the determination of oil-saturated formations in the borehole.

There is a method of determining the composition and oil and gas terrigenous rocks collectors and definitions estimation parameters based on the processing of data for different geophysical borehole sections (GIS), including the selection in the well section of the reservoir intervals, determination of their effective thicknesses, clay content and nature of the distribution of the clay material in the rock (dispersed, structural, laminated), full and effective porosity, absolute and relative permeability, evaluating oil and gas and composition extracted from hydrocarbon breed fluids, determining the displacement efficiency of oil and gas from reservoirs ("guidelines for the definition of the estimation parameters for oil and gas deposits on materials GIW with the inclusion of the results of core analysis, sampling and testing of productive layers", Ed. Boundaryscan, Vfraser, Gel, helenin, NGO "Southfromjersey", 1990, 261 S.).

The known method is implemented in accordance with the "Instructions for use materials geophysical study using the results of the study of the core and test wells to determine and justify estimation parameters for oil and gas deposits", Moscow, VNIGNI, 1987, 20 C.) and allows to determine the geological characteristics only pre-allocated in terms of the well layers of the reservoir used in the processing of readings logging for certain breeds of private collectors theoretically informed empirical petrophysical models and stochastic petrophysical relationships established on the basis of the studies taken from wells in the intervals of occurrence of rocks reservoir cores sample and analyze the relationships type core-core, core-GIS and GIS-GIS.

The known method has limitations when determining geological properties of rocks in the borehole, is used only to define the parameters of rocks reservoir and does not provide a definition of full structural-mineralogical and fluid models of the breed, and does not implement the evaluation of the geological characteristics of the rock of non-reserves in the borehole.

Closest to the invention to the technical essence is a method of determining geological properties of terrigenous rocks in the near-well space on GIS data, including the execution of geophysical surveys in the borehole and processing the received information identifying intervals collectors and assessment of their geological properties (Usagencies, Gashora, Vhuteine. The method of assessment is istoty and composition of the sand-aleurolite-clay rocks on geophysical data. Oilfield Geophysics. Issue 5. Ufa, Bashneft, 1975, p.88-94 - prototype).

There is a method allows to determine the porosity, composition and saturation Sandstone-siltstone-shale reservoirs. The method is based on the use of data processing GIS petrophysical models that take into account the impact on the values for the different methods of GIS high content in the skeleton of rock silt material and clays having different distribution (dispersed, structural, layered) in the array of the breed. During processing of GIS data to determine the coefficient of porosity, content of sand, silt and clay fractions in the skeleton of the breed, as well as the ratio of total water saturation of the rock.

The disadvantage of this method is that it is focused on the study of the properties only pre-allocated in the borehole of reservoirs and uses when processing evidence logging simplified theoretical and stochastic petrophysical models can be applied for approximate evaluation of the geological properties of rock collectors.

The objective of the invention is to increase the detail and accuracy of the determination according to the GIS geological characteristics of the rock composing the terrigenous column - definition of oil-saturated layers.

The problem is solved by the method definition wide-angle the oil reservoirs, according to which analyze log curves holes in the roof part of the productive layer, reveal layers with facile specific resistance in induction well logging (IR) of no more than 6-8 Ohm·m and indications on the curves of the neutron gamma ray (NGR) or neutron-neutron logging (NOC)of 85% or less from the values of downstream reservoirs, among the identified seams choose layers without clay jumper with layers of carbonate-saturated rocks and with the values of apparent resistivity on IR not less than 15 Ohm·m, precise lithological composition of the identified layers, when present in the composition of the rocks oil-saturated Sandstone conclude terrigenous origin of these layers, precise values of porosity, permeability and oil saturation, when exceeding the lower limits of porosity, permeability and saturation petrophysical factors for this region revealed the layers referred to as the productive.

The invention

When interpreting geophysical material having problems explaining the relatively low readings induction logging (6-8 Ohm·m) roofing part of the tournaisian tier with capacity of reservoir rocks 1-4 m below which is followed by the difference between carbonate-saturated rocks without clay lane the sliver between the layers with specific resistance, exceeding 15-20 Ohm·m

The problem is that carbonate rocks (limestone aquifer) at values of apparent resistivity on IR equal to 6-8 Ohm·m, belongs to the aquifer, and they are located above the oil-bearing strata. In between there is no insulating clay layer or interlayer, i.e., no clay jumper between layers. It turns out that below the limestone aquifer without insulating clay jumper immediately are oil-bearing limestone. This contradicts the model of oil deposits, according to which aquifers should be below the oil.

Above the oil-bearing limestone directly without the jumper be placed aquifer limestones or sandstones can't, due to the greater density of produced water compared to oil. Less dense oil due to gravitational distribution is placed above the reservoir water, as if POPs up.

The explanation of this paradox lies in the following: littp rocks with a resistivity of 6-8 Ohm·m, occurring in the oil-bearing limestone, refers to the oil-bearing terrigenous rocks (sandstones).

Description roofing (abnormal) part of the tournaisian tier shows the lowest readings curves COG or NOC compared to the underlying oil-bearing limestone (15% and is more). Such formations are widespread on Fedotov square Novo-elkhovskoye deposits in areas of erosion valleys visean age tournaisian deposits of the tier.

Choosing the right lithotype collector when interpreting will allow you to correctly determine the petrophysical parameters (porosity, permeability, clay content, saturation, and thereby increasing oil reserves and to involve them in the design. So, at the same testimony neutron gamma logging COG-60 porosity quartz Sandstone greater than the porosity of the limestone by 4-5%. This means that when determining the coefficient of saturation by the formula Archie greater coefficient of porosity at the same electrical resistivity of the layer will correspond to a larger value of the coefficient of saturation.

When the porosity coefficient of 9% and electrical resistivity of 15 Ohm·m by the formula Archie oil saturation factor of limestone tournaisian tier Novo-elkhovskoye field is 55%, this is the lower bound for the industrial-productive formations.

Oil saturation factor (KN) of the reservoir is determined by the well-known formula Archie:

KN=1/(Knm/n×Rn1/n)

where C is the proportionality coefficient equal to:

C=(a*b*RB)1/n

a, b, m, n - coefficient is eciency, defined core;

Knm/nis the coefficient of porosity formation in degreem/n.

Rn1/n- the electrical resistivity of the investigated layer degree1/n.

In the laboratory defines the electrical characteristics of core samples - parameter porosity RP and parameter saturation PH:

RP=R/R=a/Knm

PH=R/R=b/Sn

where R - electrical resistivity of the investigated layer in Ohm·m,

R - resistivity layer with videosystem in Ohm·m

R- the electrical resistivity of formation water in Ohm·m

Criteria emisions in oil in the roof part of the tournaisian tiers are as follows:

1. Induction logging. Readings 6-8 Ohm·m without the Underlying clay or compacted jumpers oil carbonate reservoirs (limestone) have this method electrical resistivity of more than 15 Ohm·m

2. Neutron methods (neutron gamma-ray logging or neutron-neutron logging. Readings roof is less than 15 percent or more compared to the underlying carbonate column.

3. Nuclear magnetic resonance logging. An index of free fluid in the reservoir, as well as in the underlying saturated carbonate rocks. That is, the reservoir and test the AI can give is contained in the pore fluid.

4. Confirmation coring terrigenous origin lithology and the nature of saturation (i.e. saturation) layer deposited without the jumper in the roof part of the tournaisian stage in two or three wells in the specific area of developed deposits of oil. When the core analysis are defined: lithology, porosity, permeability, clay content, oil and water saturation of the selected strains.

5. Calculated coefficients of porosity, permeability, clay content, the saturation on petrophysical algorithms based on terrigenous origin roof of the reservoir. When confirming the values calculated petrophysical parameters (i.e., at the close of convergence) with the data analysis of core and exceeding their largest boundary values of the coefficients for the region concludes that the roofing part of the tournaisian tier posted productive sandstones.

Specific example

In well No. 1 Fedotov square Novo-elkhovskoye field according to hydrodynamic research roofing tournaisian layer is defined at a depth of 1009,7 m

Data for well 1 are shown in table 1

In the roof part of the tournaisian stage in the interval 1009,7-1011,6 m, according to geophysical research with vain (GIS), located carbonate reservoir with porosity of 16%, oil saturation 52% (according to table No. 1 this stratum is not productive value of the coefficient of saturation) and the specific resistance of 6 Ohm·meters Below, in the interval 1011,6-1027 m is a carbonate oil reservoir with porosity 10,8%, oil saturation 71,3%, a resistivity of 19 Ohm·m According to Kern, the interval 1009,7-1011,6 m the oil-bearing sandstones. Calculated values of petrophysical parameters of reservoir sandstones in the interval 1009,7-1011,6 m according to the standard interpretation of GIS. The obtained values: the ratio of the porosity of 20%, the coefficient of saturation of 62%. I.e. the collector in the roof part of the tournaisian stage in the interval 1009,7-1011,6 m when properly determining lithology pass from the category of unproductive by the coefficient of saturation (the ratio of the saturation - 52%) in the category of productive (coefficient of saturation - 62%).

When calculating the carrying amount and recoverable oil reserves in this Deposit got the following data.

Collector carbonate (limestone). Initial reserves 80028 t, initial recoverable reserves 18406 t, the recovery factor of 23%.

The terrigenous reservoir (Sandstone). Initial reserves 133 380 t; initial recoverable reserves 66690 so the oil recovery Factor of 50%.

I.e. after the application of the proposed method when properly determining the lithology of the reservoir recoverable oil reserves increased by 48284 t, and the recovery factor of oil increased by 27%.

The application of the proposed method will allow you to identify previously undetectable oil-bearing stratum.

The method of determination of oil reservoirs, according to which, in well selected and examined Kern, conduct induction logging and neutron gamma or neutron-neutron logging, analyzing log curves holes in the roof part of the productive layer, reveal layers with facile specific resistance for induction logging no more than 6-8 Ohm·m and indications on the curves of the neutron gamma ray or neutron-neutron logging, constituting 85% or less from the values of downstream reservoirs, among the identified seams choose layers without clay jumper with layers of carbonate-saturated rocks and with the values of apparent resistivity for induction logging is not less than 15 Ohm·m, precise lithological composition of the identified layers, when present in the composition of the rocks oil-saturated Sandstone conclude terrigenous origin of these layers, precise values of porosity, permeability and oil saturation, when exceeding the lower limits of porosity, permeability and saturation petrophysical factors for this region revealed the layers referred to as productive.



 

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