Eagle Ford Shale Oil The New Buzz In South Texas Play

The Eagle Ford shale, unlike other Texas shale plays, is not just about natural gas. Producers such as Petrohawk and EOG are making some good oil wells on the north side of the trend.  The Eagle Ford, often spelled as Eagleford shale, is not uniform. It  basically is divided into three regions, which are described as the “oil window, gas condensate window, and dry gas window.

EOG Resources has focused their efforts on the oil window of the Eagle Ford shale. According to a report they recently published for investors they have indicated that the Eagle Ford shale may be one of the most significant oil discoveries in over 40 years.  

Why Is There So Much Oil In Northern Part Of  The Eagle Ford Shale?

The reason is that most of the oil stayed in the source rock (the shale).  In the oil window of the Eagle Ford some oil migrated up into the porous Austin chalk and a few good wells were drilled in the 1980′s.  Little did oil companies know then that there was literally an ocean of oil in the shale beneath the Austin chalk formation.

After all, shale was just a nuisance to be drilled through on the way to real reservoir rock such as sandstone and limestone.  Along a wide band north of the Edwards reef trend there are wide areas which were never known for oil production. It has now been recognized that there are great quantities of oil that has been sealed into the shale by impermeable rock layers above the Eagle Ford. 

In the past oil companies drilled a few wells in this area but quickly abandoned their search because the kind of geology for trapping oil in reservoirs, such as porous limestone or sandstone, simply did not exist and the technology to get oil out of the shale below had not been perfected or even imagined yet. 

 In the late 1980′s, when the Austin chalk oil boom was going on, they had horizontal drilling and hydraulic fracturing technology.  It’s just that nobody had ever considered that the two technologies could be used to recover oil and gas from shale. Finally it dawned on someone to try it in the Barnett shale and that’s where the whole revolution began. 

The map below is from Petrohawk Energy. It shows the oil window at the upper portion of the Eagle Ford shale where pressures and temperature is lower. Condensate is found in wells in the middle and lower part of the play.  All of this has to do with how underground heat and pressured cooked off the various hydrocarbons and forced some to upper formations. At the lower middle edge of the Eagle Ford shale, bordered by the Edwards Reef trend and the Sligo reef trend we see the dry gas window. Here high pressure, high volume natural gas is present and here is where Petrohawk holds the majority of their Hawkville Field property.

EOG Resources and other companies are focusing on the condensate window and the upper oil window while Petrohawk, Pioneer and Conoco are among the companies focusing on the southern gas rich, deeper end of the Eagleford shale near the Sligo reef.

EOG has drilled several test wells across a 125 mile swath of the ol window and confirmed that this will be one very widespread oilfield. One of those wells drilled just east of the old community of Zella in northwestern McMullen county is producing over 400 barrels a day.

It will be interesting to see how far the north end, the “oil window” is pushed. There will be some marginal wells and areas where it will be determined that the expense of drilling and hydraulic fracturing do not warrant completion.

Read more about EOG Resources plans for the oil window of the Eagle Ford shale:  EOG Plans