Changes

Show evaluation at the wellsite is important because it represents the first, and sometimes only, opportunity to assess the potential economic viability of a particular well or prospect. Decisions of considerable economic impact are made based on show evaluation results, including formation testing, setting pipe, participation elections, and lease acquisition or relinquishment.

Show evaluation at the wellsite is important because it represents the first, and sometimes only, opportunity to assess the potential economic viability of a particular well or prospect. Decisions of considerable economic impact are made based on show evaluation results, including formation testing, setting pipe, participation elections, and lease acquisition or relinquishment.

Mudlogs are the most useful wellsite evaluation tool due to the integration of lithology, [[rate of penetration]] (ROP), gas recordings, and oil description (see [[Mudlogging: The mudlog]]).

Mudlogs are the most useful wellsite evaluation tool due to the integration of lithology, [[rate of penetration]] (ROP), gas recordings, and oil description (see [[Mudlogging: the mudlog]]).

Wellsite show evaluation relies on the following:

Wellsite show evaluation relies on the following:

{| class = "wikitable"

{| class = "wikitable"

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|+ {{table number|1}}Types of gas that result from the drilling processa

|+ {{table number|1}}Types of gas that result from the drilling process

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! Type of Gas

! Type of Gas

=====Gas trap and agitator=====

=====Gas trap and agitator=====

This equipment is usually in or around where the flowline enters the possum belly. If the equipment is not operational (plugged orifices or lines, not powered-up, etc.), insufficient gas may reach gas analysis equipment to allow for an accurate analysis (see chapter on “Mudlogging: Gas Extraction and Monitoring”).

This equipment is usually in or around where the flowline enters the possum belly. If the equipment is not operational (plugged orifices or lines, not powered-up, etc.), insufficient gas may reach gas analysis equipment to allow for an accurate analysis (see [[Mudlogging: gas extraction and monitoring]]).

=====Gas analysis system=====

=====Gas analysis system=====

====Lag time====

====Lag time====

It is of the utmost importance to know the exact depth that all drill cuttings samples and gas are coming from within the borehole (for information on calculating lag time, see the chapter on “Wellsite Math” in Part 3).

It is of the utmost importance to know the exact depth that all drill cuttings samples and gas are coming from within the borehole (for information on calculating lag time, see [[Wellsite math]]).

==Cuttings evaluation==

==Cuttings evaluation==

In many wells, drill cuttings collected may represent the only subsurface data available for geological interpretation. After a detailed lithology description, cuttings are analyzed for hydrocarbon indications (see [[Mudlogging: Drill cuttings analysis]]). Traces of gas and oil in the cuttings represent formation hydrocarbons that have not been flushed by the [[drilling fluid]]. Gas in cuttings is analyzed by grinding a measured amount (approximately 100 mg) of unwashed cuttings in a blender, with any liberated gases analyzed by the standard gas detection system. This analysis is often divided into two components: total gas, comprising all combustible gasses; and petroleum vapors, comprising C2 through C5. This type of analysis can indicate the amount and composition of gases in the formation, even if the larger rock pores are flushed.

In many wells, drill cuttings collected may represent the only subsurface data available for geological interpretation. After a detailed lithology description, cuttings are analyzed for hydrocarbon indications (see [[Mudlogging: drill cuttings analysis]]). Traces of gas and oil in the cuttings represent formation hydrocarbons that have not been flushed by the [[drilling fluid]]. Gas in cuttings is analyzed by grinding a measured amount (approximately 100 mg) of unwashed cuttings in a blender, with any liberated gases analyzed by the standard gas detection system. This analysis is often divided into two components: total gas, comprising all combustible gasses; and petroleum vapors, comprising C2 through C5. This type of analysis can indicate the amount and composition of gases in the formation, even if the larger rock pores are flushed.

Evaluation of oil in cuttings is performed on unwashed and washed bulk cuttings and on individual grains. Evaluation includes visual inspection and analysis using a microscope and ultraviolet (UV) box. Oil shows are described by their physical properties of visual stain, fluorescence, cut, and odor. Care must be taken always to evaluate hydrocarbon shows in cuttings with respect to their petrophysical properties (see review by <ref name=pt03r45>Swanson, R. G., 1981, Sample examination manual: Tulsa, OK, [http://store.aapg.org/detail.aspx?id=603 AAPG Methods in Exploration Series No. 1], 35 p.</ref>.

Evaluation of oil in cuttings is performed on unwashed and washed bulk cuttings and on individual grains. Evaluation includes visual inspection and analysis using a microscope and ultraviolet (UV) box. Oil shows are described by their physical properties of visual stain, fluorescence, cut, and odor. Care must be taken always to evaluate hydrocarbon shows in cuttings with respect to their petrophysical properties (see review by <ref name=pt03r45>Swanson, R. G., 1981, Sample examination manual: Tulsa, OK, [http://store.aapg.org/detail.aspx?id=603 AAPG Methods in Exploration Series No. 1], 35 p.</ref>.

Activities that ''may not'' represent a show include

Activities that ''may not'' represent a show include

* A drilling break or increase in the ROP (see chapter on “Rate of Penetration”)

* A drilling break or increase in the ROP (see [[Rate of penetration]])

* An increase in the mud tank level

* An increase in the mud tank level

==See also==

==See also==

* [[Drilling problems]]

* [[Drilling problems]]

* [[Mudlogging: Drill cuttings analysis]]

* [[Mudlogging: drill cuttings analysis]]

* [[Introduction to wellsite methods]]

* [[Introduction to wellsite methods]]

* [[Wellbore trajectory]]

* [[Wellbore trajectory]]

* [[Wellsite math]]

* [[Wellsite math]]

* [[Core handling]]

* [[Core handling]]

* [[Mudlogging: Equipment, services, and personnel]]

* [[Mudlogging: equipment, services, and personnel]]

* [[Core alteration and preservation]]

* [[Core alteration and preservation]]

* [[Wellsite safety]]

* [[Wellsite safety]]

* [[Sidewall coring]]

* [[Sidewall coring]]

* [[Rate of penetration]]

* [[Rate of penetration]]

* [[Mudlogging: The mudlog]]

* [[Mudlogging: the mudlog]]

* [[Well planning]]

* [[Well planning]]

* [[Pressure detection]]

* [[Pressure detection]]

* [[Fishing]]

* [[Fishing]]

* [[Core orientation]]

* [[Core orientation]]

* [[Mudlogging: Gas extraction and monitoring]]

* [[Mudlogging: gas extraction and monitoring]]

==References==

==References==