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Old wells are gold mines

There are few frontier areas left to explore. Chances are, the area you’re working has had multiple phases of exploration by a number of companies, with a variety of mindsets. It’s a challenge to bring something new to an area that has already been picked over. Diligent integration of geology and geophysics is a must, but what has really helped me create opportunities, in a short time frame, is to build as complete a dataset as possible. What I find lacking most often is the integration of old data.

Wise old-timers will tell you the old wells are the best. In fact, new wells are potentially superior, assuming all logging runs went smoothly and the special analysis comes back in time for your next decision or well location. But old well files provide instant gratification, months if not years of work in one data package. They can de-risk a play, make (or break) a prospect, save you money, and can even enhance your reputation. They are worth more than their hardcopy weight in gold and it surprises, in fact inspires, me when old data is shrugged off as irrelevant.

Not only are old wells cheap, there is a chance you may find the data you were unsuccessful in persuading your manager, drillers, or the borehole to provide for you in your exploration campaign. New core can be especially hard to come by.

One reason old wells get overlooked is the wellfile is incomplete. Another reason is the well is completely missing and without further investigation you would not even know it existed. The older the well, the greater the potential for missing data. Wells drilled during exploration booms sometimes suffer the same affliction as filing becomes less diligent.

I have never regretted the extra effort put into bolstering my database with old, lost, or apparently missing data. A better database than your peers or predecessors will give you a good advantage. Here are some tips and advice to make the most of this inexpensive resource.

Seek the data. Persevere: missing data is missing because the last person gave up. Data has turned up in random government departments, misplaced in other wellfiles, a box of unscanned files… the list is endless. Keep a missing data list and revisit it from time to time as your understanding of data repositories evolves. For the most part I’ve found the data is not lost — it’s hiding.

Missing wells. I’ve always found at least one ‘surprise well’ in each block I have worked. I recommend you surprise yourself early before any exploration campaign. An effective method I use to check for missing wells is to overlay maps of different sources and vintage; this also is an easy way to check well locations. Another good way to reveal missing wells is to plough through both the geology and drilling and completions section of available well reports. Often references are made to past drilling campaigns. These reports usually reference the data collected — a quick check to establish if you have all the logs or special analyses available.

Location, location, location. Check locations no matter which country you’re in, what company drilled the well, or who has made the map. I’ve found high-profile wells 1 km from the actual location. Google Earth is brilliant for this kind of check. I’ve found drilling pads (squares approximately 50 × 50 m) for wells as old as 1955 in dense jungle. I recommend you have locations checked in the field. Another tip: X marks the spot. Diligent seismic operators will scout old well locations to tie with the seismic, so if you have conflicting locations for a well check to see which one is intersected by two or more lines.

Integrate and scale. Have image logs digitized or depth registered — viewing the logs in the same vertical scale is a must, and comparisons of logs is far easier when they are in the same lateral scale. Resistivity curves (usually the most consistent in old logs) are usually presented in linear scale. If I don’t have time to digitize, I will load the image into the cross section and present the digital resistivity curves in a linear scale. Linear scale resistivity is actually quite a useful correlation log in formations with less dramatic resistivity fluctuations.

Economic resolution. Times have changed since the well was drilled, thinner beds can pay out and so can tighter formations. In light of this, review the old wells. Do this at least every 10 years, or every time there is a paradigm shift in the industry.

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