The total number of horizontal Bakken wells drilled in the Elm Coulee area in Richland County, Montana is now more than 500, comprising more than 800 laterals. Since 2000 there has been a significant amount of effort spent optimizing well-completion methods. These include non-cemented and pre-perforated liners; longer laterals; cleaner fracturing fluids; staged treatments with diverters; more aggressive gel breakers; and increased proppant volumes. Well productivity has improved and costs have been reduced.

Recently operators have been experimenting with the number of laterals. The first well with three laterals was drilled in June 2004; there are now 36 wells with three laterals. The first four-lateral well was drilled in December 2004 and there are now six of those. There are even (one each) five-lateral and six-lateral wells.

How many laterals should be drilled? The authors grouped wells according to the number of laterals. Production history was summarized for each configuration and a normalized average well created. Production was then forecast taking into consideration the long-term performance of early vertical wells. Economics were then calculated. Using this approach, analysis shows that single- or dual-laterals are the most economically effective with discounted Return-On-Investment ratios of 2.0. - 2.2, as compared to about 1.6 for three or four-lateral wells.

Obviously, the limitations of the approach should be considered when interpreting results. Assumptions integral to the approach are that (1) completions technology has progressed equally across all configurations, (2) there is a homogenous reservoir with no variation between wells, and (3) lateral orientation is identical for all wells. Additional factors that the authors recommend investigating include the effect of geographical location, lateral orientation and fracturing rates and pressures. There are likely other factors too. Still, the results do show a significant economic advantage to single- or dual-lateral completions.

For further background information about the Bakken, readers are referred to the 3rd Qtr issue of PTTC Network News (www.pttc.org/newsletter/3qtr
2005/v11n3p1.htm#1) and the Rocky Mountain Region's online collection of Bakken-related information (www.
mines.edu/Research/PTTC/case
studies/). 

Excerpted from "Analysis Optimizes Well Results," Hart's E&P, November 2007, pp. 59-61.

Excerpted from "Steerable Systems Technology Advances, a supplement to Hart's E&P," Nov. 2007, pp. 24-28.

There are two widely used constant bottomhole circulating methods—the Driller's Method and the Wait and Weight (W&W) method. The basic principle of both methods is to keep bottomhole pressure (BHP) constant at or, preferably, slightly above the formation pressure. A common question is: Which method is best to use?

Two circulations are required with the Driller's Method. During the first circulation, the mud is circulated out

with the original mud weight. Constant BHP during the first circulation is maintained by holding circulating drill pipe pressure constant. If the original mud weight is insufficient to balance the formation pressure, the well is killed by circulating a heavier mud. To hold BHP constant during the second circulation, one of two procedures can be used. The W&W method, which is considered more complex because of the calculations required, involves only one circulation where the influx is circulated out and the kill mud pumped in.

The article's Chevron authors considered several scenarios, including among others deviated hole/tapered drill string, hole problems, fluid mixing capability of rigs, drilling in formations with ballooning potential, complications and friction changes during well control, shoe pressure, maximum casing pressure at surface and peak gas flow rate. Considering all factors, the authors conclude that, due to the low experience level of current drilling staff, limited field practice with well control, and exaggerated and often unachievable benefits with the W&W method, the Driller's Method offers advantages. Additionally, there are certain conditions (ballooning, swabbed kicks, hydrate concerns in deepwater, hole stability problems) that dictate that only the Driller's Method should be used.

Excerpted from "Driller's Method Vs. Wait and Weight Method: One Offers Distinct Well Control Advantages," Drilling Contractor, November/December 2007, pp. 68-74.

Shambhu Energy LLC, Tulsa, OK, assisted Century Geophysical Corporation in 2007 in developing a spectral neutron logging tool that will measure the spectrum of neutron-induced gamma rays emitted by the elements of the subsurface formation using a scintillation detector. The spectral neutron log, at very low cost, can identify fluid-type behind casing in reservoirs. It can also provide lithology information from the display of the measured gamma ray spectrum, determine and monitor oil and water and gas and water contact through the life of a producing well, and evaluate the hydrocarbon content of a well before plug and abandonment. The spectral neutron log can also identify and evaluate coal beds and coal bed methane.

For further information or to arrange for spectral neutron logging services, please contact: Dr. Shambhu N. Tripathi, Shambhu Energy LLC by phone 918.320.1163 or via email shambhuenergy@gmail.com.