Method For Quantitatively Assessing Connectivity For Well Pairs At Varying Frequencies

• US 20130042677A1
• Filed: 07/01/2010
• Published: 02/21/2013
• Est. Priority Date: 10/20/2009
• Status: Active Grant

• Current Assignee: Charlie S. Kim, David M. Chorneyko, John W. Snedden, Neal L. Adair
• Original Assignee: Charlie S. Kim, David M. Chorneyko, John W. Snedden, Neal L. Adair
• Inventors: Adair, Neal L., Snedden, John W., Chorneyko, David M., Kim, Charlie S.
• Granted Patent: US 9,169,726 B2
• Time in Patent Office: Days
• US Class Current: 73/152.54
• CPC Class Codes: E21B 41/00 Equipment or details not covered by groups E21B15/00 - E21B40/00
• CPC Class Codes: E21B 47/00 Survey of boreholes or wells monitoring pressure or flow of drilling fluid E21B21/08
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
• CPC Class Codes: E21B 49/008 by injection test; by analysing pressure variations in an injection or production test, e.g. for estimating the skin factor measuring pressure E21B47/06
• CPC Class Codes: G01V 2210/644 Connectivity, e.g. for fluid movement
• CPC Class Codes: G01V 2210/65 Source localisation, e.g. faults, hypocenters or reservoirs
• CPC Class Codes: G01V 2210/66 Subsurface modeling

Abstract

Method for quantitatively assessing connectivity for well pairs at varying frequencies. A time series of measurements (12) is chosen for each of the two wells such that the particular measurements will be sensitive to subsurface connectivity if it exists (11). The two time series may then be pre-processed by resampling to time intervals commensurate with response time between the two wells (13), detrending the measurements (14), and detecting and eliminating spiking noises (15). Then the time series are transformed to the frequency domain where coherence and phase between the two series are compared for varying frequencies (16). This comparison is used to make a determination of connectivity.

Claims

1. A method for quantitatively assessing connectivity between two wells in a subsurface region for the purpose of planning or managing production of hydrocarbons from the subsurface region, comprising comparing spectral content of a time series of measurements from one well to spectral content of a time series of measurements from the other well.

2. The method of claim 1, wherein said comparison between wells of spectral content of time series of measurements comprises:

(a) obtaining for each of the wells a time series of measurements characterizing a physical or operating condition of the well, said physical or operating condition being selected to show coherence between the two wells only if the wells are hydraulically connected through the subsurface region;

(b) estimating either cross-spectral coherence or both cross-spectral coherence and phase of the two time series;

(c) quantitatively assessing connectivity between the two wells using the estimated coherence or the estimated coherence and phase; and

(d) planning or managing production of hydrocarbons from the subsurface region using the well connectivity assessment.

3. The method of claim 2, wherein estimating cross-spectral coherence and phase of the two time series comprises transforming autocorrelation and cross-correlation of the two time series to frequency domain, then from that, determining coherence and phase of the two series at a plurality of frequencies to produce a coherence spectrum and a phase spectrum.

4. The method of claim 2, further comprising resampling the two time series with sampling intervals based on estimated response time between the two wells, and using the two resampled time series in the estimating of coherence or phase.

5. The method of claim 4, further comprising detrending and normalizing the two time series before the estimating of coherence or phase.

6. The method of claim 5, further comprising detecting and deleting spiking noises in the two time series of measurements before the estimating of coherence or phase.

7. The method of claim 2, wherein the physical condition of the well is pressure or temperature.

8. The method of claim 2, wherein the operating condition of the well is injection rate, production rate, or flow rate.

9. The method of claim 2, wherein coherence or phase is estimated by a mathematical computation of cross-spectral coherence or phase, yielding numerical values of coherence or phase at varying frequencies.

10. The method of claim 4, wherein the resampling comprises determining new sampling time intervals, said new intervals being longer than time intervals in the two time series of measurements, and the measurements are sampled using an average of values in a sampling interval.

11. The method of claim 6, wherein detecting and deleting spiking noises in the time series of measurements comprises applying a time window to the series, said time window containing a plurality of time intervals and associated measurement values of the series, including a central measurement value located at the window'"'"'s middle, then computing a median value of the measurements within the window and replacing the central measurement value by the median value if the difference between the median value and the central measurement value exceeds a pre-determined threshold value.

12. The method of claim 11, wherein the window includes 2N+1 time intervals of the measurement series, where N is an integer.

13. A method for quantitatively assessing connectivity between two wells in a subsurface region for the purpose of planning or managing production of hydrocarbons from the subsurface region, comprising:

(a) obtaining for each of the two wells a time series of measurements characterizing a physical or operating condition of the well, said physical or operating conditions being selected to show coherence between the two wells only if the wells are hydraulically connected through the subsurface region;

(b) pre-processing the two time series of measurements by performing one or more of;

resampling the two time series with sampling intervals based on estimated

response time between the two wells;

detrending and normalizing the two time series; and

detecting and deleting spiking noises in the two time series of measurements;

(c) estimating either coherence, or both coherence and phase, between the two pre-processed time series;

(d) assessing connectivity between the two wells using the estimated coherence or using both the estimated coherence and phase; and

(e) planning or managing production of hydrocarbons from the subsurface region using the well connectivity assessment.

14. The method of claim 13, wherein coherence or phase is estimated by a mathematical computation of cross-spectral coherence or phase, yielding numerical values of coherence or phase at varying frequencies.

15. The method of claim 13, wherein coherence is estimated by plotting the two time series and performing a visual inspection.