Shale Heterogeneity…a Surprise?

Posted on November 25, 2013

0


shale porosity

Monday has become my favourite day at the Department of Petroleum and Geosystems Engineering (PGE) at the University of Texas at Austin (UT). The reason is that every Monday at 3 PM they hold what they call a “Graduate Seminar” that Ph.D. students must attend. Of course, these seminars are very interesting for the rest of us as well. They also have a tradition that from 10 AM to 12 PM and from 1 PM to 3 PM it is possible to book a one-on-one 30 minute private conversation with the seminar speaker. The faculty’s teaching staff usually also have a joint sandwich lunch with the speaker. It would be interesting to do something similar in Uppsala.

The reason I am describing this now is that today there was a fantastically interesting presentation given by Carl Sondergeld, Professor and the Mewbourne Chair, Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma. The title was, “Shale Heterogeneity…a Surprise?”. Here is the abstract for his presentation:

Shale is defined based on grain size (~4μm); there is no restriction on coposition. Often associated with this particle size are clays and organics. World average mineralogies suggests shales are dominated by quartz and clays. Clearly, the Eagle Ford and Niobrara are notable exceptions. Drilling and completion activity indicates that only 25-30% of shale acreage is “core.” Furthermore, in those core areas, rock quality as reflected in production appears quite variable. Analysis of the stage efficiency suggests 30-40% of stages are ineffective. A recent EIA shale study has downgraded the reserves of a number of resource plays in recognition of the impact of “shale heterogeneity.” Imagine an operator with a 2000 well program where each completion involves 10 stages but only 7 out of 10 are actually productive. If each stage costs about $100,000, he is wasting roughly $600,000,000. If we could save on average 1 stage per well, he would save $200,000,000 and the attendant lost time to complete 2000 stages. Shale heterogeneity occurs at all scales: basin wide, seismic, outcrop, wellbore, core, plugs, thin section and SEM and TEM scales. Furthermore heterogeneity is manifest in matrix composition, fractures, hydrocarbon volumes and petrophysical properties. Heterogeneity presents challenges in its assessment and quantification as well in completion strategies. These challenges are exacerbated by the need to reduce costs, reluctance to retrieve core, and the limited logging executed in horizontal boreholes. It would be useful to assess heterogeneity as the drillbit progresses; however, the resulting cuttings, a byproduct of drilling, are compromised by the widespread use of PDC bits. The cuttings are extremely small and mechanically compromised rendering them almost useless for petrophysical and mechanical studies. So then, how can we assess shale heterogeneity in a time frame to impact decisions? A partial answer lies in the growing suite of downhole measurement tools. After examining examples of heterogeneity, I will discuss technologies and strategies which with minor modifications can address this issue. Coupling new drillbit technologies with classical petrophysical measurement techniques as well as new techniques can take us a long way in addressing the shale variability which could factor directly into completion strategies.

Of special interest were his comments that the hopes for shale oil and gas production outside of the USA were overly optimistic. Regarding Europe he thought that it would not become reality. He was also very doubtful regarding production of shale gas in Australia. For some reason he said that every borehole was twice as expensive to drill there compared to the cost in the USA. The fact that Australia has no domestic need for the shale gas is another hindrance. However, he thought that production of shale gas might become reality in China.

(Swedish)

Måndagar har blivit min favoritdag vid institutionen för “Petroleum and Geosystems Engineering”, PGE, University of Texas at Austin, UT. Anledningen är att man varje måndag klockan 15:00 har vad man kallar för ”Graduate Seminar” där doktorander har närvaroplikt. Självklart är dessa seminarier mycket intressanta för oss övriga. Man har också traditionen att från 10 till 12 och 13 till 15 kan vi boka in oss för att ha ett privat samtal med föredragshållaren, 1 to 1, under en halvtimma. Fakultetens lärare brukar också ha en gemensam smörgåslunch med föredragshållaren. Skulle vara intressant att ha något liknande i Uppsala.

Att jag berättar om detta nu är dagens fantastiskt intressanta fördrag som hölls av Carl Sondergeld, Professor and the Mewbourne Chair, Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma. Titeln var: “Shale Heterogeneity…a Surprise?”. Här är hans abstract till föredraget:

Shale is defined based on grain size (~4μm); there is no restriction on coposition. Often associated with this particle size are clays and organics. World average mineralogies suggests shales are dominated by quartz and clays. Clearly, the Eagle Ford and Niobrara are notable exceptions. Drilling and completion activity indicates that only 25-30% of shale acreage is “core.” Furthermore, in those core areas, rock quality as reflected in production appears quite variable. Analysis of the stage efficiency suggests 30-40% of stages are ineffective. A recent EIA shale study has downgraded the reserves of a number of resource plays in recognition of the impact of “shale heterogeneity.” Imagine an operator with a 2000 well program where each completion involves 10 stages but only 7 out of 10 are actually productive. If each stage costs about $100,000, he is wasting roughly $600,000,000. If we could save on average 1 stage per well, he would save $200,000,000 and the attendant lost time to complete 2000 stages. Shale heterogeneity occurs at all scales: basin wide, seismic, outcrop, wellbore, core, plugs, thin section and SEM and TEM scales. Furthermore heterogeneity is manifest in matrix composition, fractures, hydrocarbon volumes and petrophysical properties. Heterogeneity presents challenges in its assessment and quantification as well in completion strategies. These challenges are exacerbated by the need to reduce costs, reluctance to retrieve core, and the limited logging executed in horizontal boreholes. It would be useful to assess heterogeneity as the drillbit progresses; however, the resulting cuttings, a byproduct of drilling, are compromised by the widespread use of PDC bits. The cuttings are extremely small and mechanically compromised rendering them almost useless for petrophysical and mechanical studies. So then, how can we assess shale heterogeneity in a time frame to impact decisions? A partial answer lies in the growing suite of downhole measurement tools. After examining examples of heterogeneity, I will discuss technologies and strategies which with minor modifications can address this issue. Coupling new drillbit technologies with classical petrophysical measurement techniques as well as new techniques can take us a long way in addressing the shale variability which could factor directly into completion strategies.

Särskilt intressant var hans kommentarer om att shaleproduktion utanför USA är överdrivet optimistiska. Vad det gäller Europa ansåg han att den inte kommer att bli verklighet. Han var också mycket tveksam till skiffergasproduktion i Australien. Av någon anledning sa han att varje borrhål var dubbelt så dyrt att borra där jämfört med kostnaden i USA. Detta faktum och att Australien inte har ett inhemskt behov är hämmande faktorer. Vad det gällde skiffergas i Argentina så var det inget företag som gick med vinst. Kvar återstår Kina och där trodde han att produktionen blir verklighet.

Posted in: Uncategorized