Thursday, April 27, 2017

Python, wells, LAS and info

Those of you who deal with wireline well log data know that the standard format is call LAS. A nice site from the Canadian Well Logging Society that explains the format can be found here. In the old days, a well would be logged for gamma ray, density and maybe a couple of electric logs. In today's world, a full logging assault can yield a vast collection of data types (called curves). Not only that, but these might be split across many LAS files. One well in our data base has 17 LAS files! Each individual curve has a short abbreviation (a mnemonic) such as GR (gamma ray), RHOB (bulk density) and DT (compressional sonic). The mnemonics are somewhat standardized, but in fact there is broad variability between logging companies. Each curve also has units and a description field in the LAS file.

How do you figure out what curves are contained in such a collection of LAS files? Well, one approach is to convert each LAS to an excel file, but that gets messy and brings in the data as well as the curve information. The Agile Geoscience folks have discussed this topic and python in detail; here we have a less ambitious goal that allows a simple solution.

To deal with this problem, I wrote a code in python that I call info.py - here it is

import lasio
import os

n = 1
for file in os.listdir("."):
    if file.endswith(".las") or file.endswith(".LAS"):
        var = lasio.read(file)
        print "\n las"+str(n), file
        print var.well
        print var.other
        for curve in var.curves:
            print("%s\t[%s]\t%s\t%s" % (curve.mnemonic, curve.unit, curve.value, curve.descr))
        n += 1

This little code is magic, mainly because it draws on lasio, a library for reading and writing LAS files. Stepping through the code line-by-line goes like this
  1. import the lasio library
  2. import the operating system library
  3. set counter n to 1
  4. for each file in the current directory...
  5. if the file name ends in las or LAS...
  6. read the file
  7. print 'las' with n appended, then the file name
  8. print the 'well' data section of the file
  9. print the 'other' data section of the file
  10. for each curve in the file print mnemonic, units, value and description
  11. increase n by 1 and continue till all files are read
My early versions of this code required the file names to be pasted into the code, which was ok for a few LAS files. But that got very clunky with more than four files.

I work on a mac which has a command line terminal and python build in. Python has lots of default libraries, but others are always needed. I install them with pip, but first you must install pip itself

sudo easy_install pip

Then this command line installs lasio

sudo pip install lasio

Now you are ready to go. The code above can be copied into a text editor and saved as info.py (or another name you like better). Now go to a directory full of LAS files from a well and copy info.py into that folder. On the mac, open a terminal window and cd to the LAS directory, then type

python info.py

or, if you want to capture the output into a file

python info.py > info_jones1a.txt

The result will look something like the listing at the end of this post. The beauty of this little code fragment is the amount of information it makes readily available in complex well situations with many, or redundant, or overlapping LAS files. 

Hope you enjoy the code and it helps you organize a few tough LAS situations.

las1 Jones_1A_run1.las

Mnemonic  Unit  Value                       Description      
--------  ----  -----                       -----------      
STRT      F      437.0                      START DEPTH      
STOP      F     4000.5                      STOP DEPTH       
STEP      F     0.5                         STEP             
NULL            -999.25                     NULL VALUE       
COMP            Jones                       COMPANY          
WELL            1A                          WELL             
FLD             WILDCAT                     FIELD            
LOC             SHL: 1320' FNL & 2210' FWL  LOCATION         
CNTY                                        COUNTY           
STAT                                        STATE            
CTRY                                        COUNTRY          
SRVC                                        SERVICE COMPANY  
API                                         API NUMBER       
DATE            8-Jun-2012                  LOG DATE         
UWI                                         UNIQUE WELL ID   

DEPT [F] DEPTH (BOREHOLE) {F12.4}
C1 [IN] Caliper 1 {F11.4}
C2 [IN] Caliper 2 {F11.4}
CDF [LBF] Calibrated Downhole Force {F11.4}
CTEM [DEGF] Cartridge Temperature {F11.4}
DCAL [IN] Differential Caliper {F11.4}
DEVI [DEG] Hole Deviation {F11.4}
GR_EDTC [GAPI] EDTC Gamma Ray {F11.4}
GTEM [DEGF] Generalized Borehole Temperature {F11.4}
HAZI [DEG] Hole Azimuth {F11.4}
HAZIM [DEG] Hole Azimuth {F11.4}
P1AZ [DEG] Pad 1 Azimuth {F11.4}
RB [DEG] Relative Bearing {F11.4}
SDEV [DEG] Sonde Deviation {F11.4}
SDEVM [DEG] Sonde Deviation {F11.4}
STIT [F] Stuck Tool Indicator, Total {F11.4}
TENS [LBF] Cable Tension {F11.4}

las2 Jones_1A_run2.las

Mnemonic  Unit  Value                       Description      
--------  ----  -----                       -----------      
STRT      F      437.0                      START DEPTH      
STOP      F     4000.5                      STOP DEPTH       
STEP      F     0.5                         STEP             
NULL            -999.25                     NULL VALUE       
COMP            Jones                       COMPANY          
WELL            1A                          WELL             
FLD             WILDCAT                     FIELD            
LOC             SHL: 1320' FNL & 2210' FWL  LOCATION         
CNTY                                        COUNTY           
STAT                                        STATE            
CTRY                                        COUNTRY          
SRVC                                        SERVICE COMPANY  
API                                         API NUMBER       
DATE            8-Jun-2012                  LOG DATE         
UWI                                         UNIQUE WELL ID   

DEPT [F] DEPTH (BOREHOLE) {F12.4}
AF10 [OHMM] Array Induction Four Foot Resistivity A10 {F11.4}
AF20 [OHMM] Array Induction Four Foot Resistivity A20 {F11.4}
AF30 [OHMM] Array Induction Four Foot Resistivity A30 {F11.4}
AF60 [OHMM] Array Induction Four Foot Resistivity A60 {F11.4}
AF90 [OHMM] Array Induction Four Foot Resistivity A90 {F11.4}
AO10 [OHMM] Array Induction One Foot Resistivity A10 {F11.4}
AO20 [OHMM] Array Induction One Foot Resistivity A20 {F11.4}
AO30 [OHMM] Array Induction One Foot Resistivity A30 {F11.4}
AO60 [OHMM] Array Induction One Foot Resistivity A60 {F11.4}
AO90 [OHMM] Array Induction One Foot Resistivity A90 {F11.4}
AT10 [OHMM] Array Induction Two Foot Resistivity A10 {F11.4}
AT20 [OHMM] Array Induction Two Foot Resistivity A20 {F11.4}
AT30 [OHMM] Array Induction Two Foot Resistivity A30 {F11.4}
AT60 [OHMM] Array Induction Two Foot Resistivity A60 {F11.4}
AT90 [OHMM] Array Induction Two Foot Resistivity A90 {F11.4}
AHFCO60 [MM/M] Array Induction Four Foot Conductivity A60 {F11.4}
AHMF [OHMM] Array Induction Mud Resistivity Fully Calibrated {F11.4}
AHORT [OHMM] Array Induction One Foot Rt {F11.4}
AHORX [OHMM] Array Induction One Foot Rxo {F11.4}
AHSCA [MV] Array Induction SPA Calibrated {F11.4}
AHTCO10 [MM/M] Array Induction Two Foot Conductivity A10 {F11.4}
AHTCO20 [MM/M] Array Induction Two Foot Conductivity A20 {F11.4}
AHTCO30 [MM/M] Array Induction Two Foot Conductivity A30 {F11.4}
AHTCO60 [MM/M] Array Induction Two Foot Conductivity A60 {F11.4}
AHTCO90 [MM/M] Array Induction Two Foot Conductivity A90 {F11.4}
AHTD1 [IN] Array Induction Two Foot Inner Diameter of Invasion(D1) 
AHTD2 [IN] Array Induction Two Foot Outer Diameter of Invasion (D2) 
AHTRT [OHMM] Array Induction Two Foot Rt {F11.4}
AHTRX [OHMM] Array Induction Two Foot Rxo {F11.4}
CDF [LBF] Calibrated Downhole Force {F11.4}
CFTC [HZ] Corrected Far Thermal Counting Rate {F11.4}
CNTC [HZ] Corrected Near Thermal Counting Rate {F11.4}
CTEM [DEGF] Cartridge Temperature {F11.4}
DCAL [IN] Differential Caliper {F11.4}
DNPH [CFCF] Delta Thermal Neutron Porosity {F11.4}
DPHZ [CFCF] HRDD Standard Resolution Density Porosity {F11.4}
DSOZ [IN] HRDD Standard Resolution Density Standoff {F11.4}
ECGR [GAPI] Environmentally Corrected Gamma-Ray {F11.4}
GDEV [DEG] HGNS Deviation {F11.4}
GR [GAPI] Gamma-Ray {F11.4}
GTEM [DEGF] Generalized Borehole Temperature {F11.4}
HCAL [IN] HRCC Cal. Caliper {F11.4}
HDRA [G/C3] HRDD Density Correction {F11.4}
HDRB [G/C3] HRDD Backscatter Delta Rho {F11.4}
HGR [GAPI] HiRes Gamma-Ray {F11.4}
HMIN [OHMM] MCFL Micro Inverse Resistivity {F11.4}
HMNO [OHMM] MCFL Micro Normal Resistivity {F11.4}
HNPO [CFCF] HiRes Enhanced Thermal Neutron Porosity {F11.4}
HPRA [] HRDD Photoelectric Factor Correction {F11.4}
HTNP [CFCF] HiRes Thermal Neutron Porosity {F11.4}
NPHI [CFCF] Thermal Neutron Porosity (Ratio Method) {F11.4}
NPOR [CFCF] Enhanced Thermal Neutron Porosity {F11.4}
PEFZ [] HRDD Standard Resolution Formation Photoelectric Factor 
PXND_HILT[CFCF] HILT Porosity CrossPlot {F11.4}
RHOZ [G/C3] HRDD Standard Resolution Formation Density {F11.4}
RSOZ [IN] MCFL Standard Resolution Resistivity Standoff {F11.4}
RWA_HILT[OHMM] HILT Apparent water resistivity {F11.4}
RXO8 [OHMM] MCFL High Resolution Invaded Zone Resistivity {F11.4}
RXOZ [OHMM] MCFL Standard Resolution Invaded Zone Resistivity {F11.4}
SP [MV] Spontaneous Potential {F11.4}
SPAR [MV] SP Armor Return {F11.4}
STIT [F] Stuck Tool Indicator, Total {F11.4}
TENS [LBF] Cable Tension {F11.4}
TNPH [CFCF] Thermal Neutron Porosity {F11.4}

Tuesday, April 25, 2017

Carbonate Essentials Webinar - Day 1

Had a very good session with several questions. We had 28 attendees, but some of them were group logins. Total registration is 50. Tomorrow is part 2!

Screen shot of the webinar in progress. Attendee names redacted to protect the innocent. 
You can always depend on Mike Graul for a good dose of humor.

Wednesday, March 22, 2017

Geological modeling in python

Latest results will be posted here at the top as progress warrants...

==== 22 Mar 2017 ====


Now we are getting somewhere! Improvements here include long and short wavelength variation on basement and Mississippian unconformities, realistic level of noise added, two Penn limestone beds and a late monocline down to the left. The monocline is the first function for a new function called bender that will include monoclines, bumps and dip. Remember, the idea is not to reproduce this particular field line in all it's detail, but to reproduce essential characteristics and trace them back to the earth model. For example, the shallow Penn LS event on field data is a seismic thin bed as evidenced by a 90 degree phase shift. Either rock properties, thickness or both will have to be changed since this phase shift is not seen in model data. Also, was able to load a model 2D line into OpendTect, leading toward the real goal...3D!!


==== 6 Mar 2017 ====
Low impedance weathered LS zone is now partially embedded in LS at the unconformity, give better fit to amplitude variation observed in real data.


Note isolated doublet at high point of unconformity surface that might be interpreted as a sinkhole is actually a LS outlier underlain by weathered LS


--------------- original 9 Mar 2017 blog entry ---------------------------

For some time I have been considering the difficulty of making realistic geological models for input to seismic modeling. There are no good tools out there, despite half of century of clear need. Oh sure, there are some computational geometry packages that can model anything from a space ship to the Rocky Mountains given enough time and money, and geostatistical packages that rarely make geologically realistic models. One approach would be to mimic nature and start with a granite surface, deposit sediments, follow a sea level curve, subside, uplift, erode, preserve, and so on. Appealing from a 'let's completely replicate nature' viewpoint,  but would require a vast number of parameters to control everything.

The goal, for me, is to generate 3D seismic data with a level of geological realism that makes it suitable for seismic interpretation training. After all, in this scenario the answer is known -- the geological earth model in depth and time consisting of P-wave, S-wave and density at every sample point. I am more in the camp of video gamers who construct complex and realistic landscapes with a bag of tricks and simple algorithms. The simplest code that creates to most realistic result, that is the goal.

The specific object of my current attention is US mid-continent data typical of NE Oklahoma where my U Arkansas geosciences department has several donated 3D seismic surveys. You can find an image of a typical seismic profile here. From bottom up, key elements are: (1) a granitic basement unconformity with significant relief and a weathered granite conglomerate of irregular thickness, (2) Cambrian through Mississippian carbonates, thickly layered and laterally consistent, (3) a major unconformity at the Miss-Penn boundary with rugged relief and a low velocity, low density, deeply weathered, irregular thickness unit sitting on the unconformity surface, and (4) Pennsylvanian sandstone units of laterally variable thickness and properties with shale between sandstone units with slightly vertically variable parameters. Here is an example:


Of particular interest is the issue of subtle structural distortion on seismic time data due to overlying stratigraphic lateral variations. This kind of distortion cannot be fixed by prestack depth migration unless the migration velocity field is exquisitely precise, which is not currently achievable. Perhaps full waveform inversion my deliver that kind of velocity model someday. But till then, we are left with subtle structures that may be false closures and tempting drill targets.

I wanted to do all this for research interest and as a python learning exercise. Depth-to-time conversion and some display are done with SeismicUnix, everything else in python. My first examples were pretty crude (Figures 1 and 2 below). Too simplistic for interpretation exercises.

After months of head scratching, python learning and geological sketches, the result is getting to a realistic level of complexity (Figures 3-5). I learned about bumpy, nymph arrays in N dimensions, loops, conditionals, and how to write a files. Still stumped on writing binary files that can be read by SeismicUnix, so everything is text files so far but I think this will not work in 3D. So more learning ahead. Simulation of seismic vertical resolution is accomplished by convolution with a wavelet and lateral resolution by smoothing to bin size before depth conversion and convolution. Still needs improvement, still only 2D, but a much more realistic result. With a bit more progress and the jump to 3D, these earth models can be used to study issues related to subtle false structure, vertical and lateral resolution, effect of sub resolution features, interpretation methods for stratigraphic targets and depth conversion for subtle structure.

The thought of doing all this in C is daunting to the point I would not have tried it, even with the SeismicUnix C environment as a framework. Long live python.

Figure 1. Earth parameter modell in depth from early effort in Nov 2016. The Miss-Penn unconformity and chat layer on it look pretty good though. This early version did not have a basement unconformity.


Figure 2. P-wave model in time and the noise-free seismic response for earth model in Fig 1. Note the subtle structure for layers below the prominent Miss-Penn unconformity, even though the depth model above shows these beds are horizontal.
Figure 3. Current code P-wave velocity model in depth. Now we have a basement unconformity, a basal conglomerate of variable thickness and many Penn sandstone layers cut into shale or earlier sandstone units.
Figure 4. Current code earth model in P-wave time.

Figure 5. Current code noise-free seismic response for earth model in Fig 4. The Penn section may be a bit overcooked, but that can be controlled by a few parameters. At lease we now see the characteristic wormy appearance typical of complex sand-shale sequences worldwide and false structure for deep events.