Influence of the Linear Filtration Law Breach on the Gas-Liquid Mixtures Influx Into the Well

Podkorytova E.O., Skorikov S.D., Smovge A.

Tyumen State Oil and Gas University, Tyumen, Russia

[e-mail]

Many practical examples of the well testing (at the Yamburg, Urengoy and other fields in Tyumen) show, that the production curves, by no means always take the shape of a line on the graphs «depression squared – flow rate».

The indicators curves (IC) distortion often occurs not due to the filtration law breach, but due to the fact that a considerable influence of a number of parameters changes that not taken into account: such as super compressibility factor - Z(P,T), viscosity - (P, T), volume factor - B(P, T) and density - (P,T), where P - borehole pressure, T - temperature.

Well known modern methods for this analyzing there date of well testing are not taking consideration the fact that during bilinear, linier and radial filtration gas in fracture and in reservoir may be situations when in the different parts of zones of filtration occurs under the conditions of Darcy’s law breach or not.

The methods for planning and analyzing results of gas well testing, in which early there was realized hydraulic fracture today deal with using methods developed by Gringarten, Cinco-Ley and et. Their methods proposed using type curves and calculations parameters of reservoir by comparing filed curves received during well testing with type curves.

So may be determined as time for realization well testing hydraulic fractured well, so as select adequate model during analyzing process of filtrations.

The influences of all the pointed out factors on the IC and pressure built-up curves (PBU) behavior for hydraulic fractured well is particularly special.

The basic equation used at the analysis of results of gaugings is the Darcy law, which for a radial flow has the form:

ΔР = Pi –Р w = Q•μ/(2•π•k•h) ln (re /rw). (1)

where Pi – initial pressure, P – wellbore pressure, Q – rate, µ - viscosity of gas, k - permeability, h – thickness of layer, re – radius of external, rw – well radius.

As in calculations it is necessary to take into consideration surface gaugings rates for recalculation on wellbore pressure the volume factor.

The equation (1) precisely enough characterizes process of movement of a liquid in a layer at small depressions. At schedule construction in coordinates as ∆Р – Q, and in coordinates ∆Р2 - Q – curve IC is strongly bent downwards (fig.).

Fig. Examples IC for a case of infringement of the law of a filtration (Darcy)

And only on the schedule (∆Р2)/Q-f (Q) we receive again a straight line, as on fig. The display curve begins not with the beginning of coordinates, and recedes on an axis of abscises on distance equal to A. By this piece (A) probably definition transmissibility a layer.

At the same time, numerous researches of wells as on Urengoj, Yamburg and other reservoir that the real data no means always coincide with the laws accepted here.

Difference is especially striking at research gas condensate deposits.

We must take into account this particularity during interpretation date of well testing.

GEOPHYSICS

WELL-LOGGING

Lateral Log signals in deviated and horizontal wells (based on numerical modeling data)

Arzhantsev V.S.

A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia

[e-mail]

The accurate estimation of geoelectric parameters which allows to correct petrophysical evaluation of hydrocarbon saturation of composite oil and gas formations drilled by horizontal wells is a difficult task of well logging today. Lateral Log (Russian Log) data can be useful in solving this problem. Lateral log is widely used in well logging for almost 50 years. Also it has a rich interpretation database, but the new data received in highly deviated and horizontal wells demand in a new theoretical base and interpretational technique.

It is necessary to take into account low formation thickness, resistivity distribution from top to bottom of the layers. Deviation of the wellbore, it’s profile ellipticity, low resistivity of drilling mud, eccentricity of the tool and finite sizes of sondes are also affects on Lateral log signals. Therefore the choice of the most appropriate geoelectrical model will significantly improve evaluation reliability of geoelectrical parameters of investigated objects.

There are increasing importance of utilizing Lateral Log within the Complex which is delivered downhole on the drilling tool or tubing (“SKL” tool), including the wells with a horizontal completion.

The objects of this research are geoelectrical parameters of geological features (terrigenous cross-sections of central part of Western Siberia) determined by Lateral logging data in highly deviated and horizontal wells.

It was performed 2D modeling for the oil reservoir which crossing by horizontal well at different positions and performed calculations of sensitivity functions of Lateral sondes to formation parameters also it was created empirical charts for Lateral sondes for 1D homogeneous formations with low mud resistivity.

It was obtained a series of synthetic diagrams in horizontal wells and found strong effect of borehole profile ellipticity and no effect of tool eccentricity on Lateral Log sonde’s signals.

It was found that in highly deviated and horizontal wells Lateral Log curves becomes symmetric relative to the center of observed formation.

Author restored geolelectric parameters for a number of field (practical) diagrams using 3D modeling inversion data.

References:

1. 3D Mathematical Modelling of Harmonic Electromagnetic Fields in Problems of Logging in Deviated-Horizontal Well Surodina I.V., Epov M.I., Martakov S.V. // International Conference on Matematics 2004. Part.2. p. 699-703.

2. Solution of the problem of Lateral Log in deviated wells by integral equation method. Tabarovskiy L.A., Dashevskiy Y.A. Geology & Geophysics, №7. (1976)

3. Apply 2-D Rapid Iterative Inversion for Lateral Resistivity Logs. Wei Yang, Qingdong Shi. SPWLA 40 th Annual Logging Symposium, May 30-June3, 1999

4. Inversion of a Lateral Log Using Neural Networks. Gerardo Garcia and Whitman W.W.,* Walt Whitman Software Inc. 1992

5. Estimation of Resolution of the Electromagnetic Methods. Tabarovskiy L.A., Epov M.I. Geology & Geophysics, №5. (2006)

6. Enhanced Interpretation of Russian and Old Electrical Resistivity Logs Using Modeling and Inversion Methods. Frenkel M. A., Mezzatesta A.G. SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, 5–8 October 1997.

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