Resistivity-Based Pore-Pressure Prediction—Pitfalls and Solutions

Saleh, Saad; Williams, Ken; Rizvi, AiJaz

doi:10.2118/166105-ms

Cited by 4 publications

(2 citation statements)

References 9 publications

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“…Wilson et al (2005) reviewed the wellbore stability challenges faced in the Pompano field in deepwater GOM. Saleh et al (2013aSaleh et al ( , 2013bSaleh et al ( , 2013cSaleh et al ( , and 2013d) provide analysis of pore-pressure prediction issues in subsalt sediments, which can be helpful to reduce drilling risks.…”

Section: Rubble Zone Drilling Practices and Hazardsmentioning

confidence: 99%

Rubble Zone Below Salt: Identification and Best Drilling Practices

Saleh¹,

Williams

Rizvi

2013

Day 3 Wed, October 02, 2013

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A joint-industry project (JIP) from 2005 through 2009 involved acquiring, analyzing, and documenting more than 100 subsalt wells in the Gulf of Mexico (GOM), from shelf to deepwater. The result of this unique study culminated in the compilation of a large and comprehensive database of pertinent petrophysical, geophysical, and drilling data. This database was used to develop a set of suggested best practices for pore-pressure estimation below and around salt bodies. An analysis of the wells in the subsalt JIP indicated that the majority (64%) of the wells studied demonstrated evidence of a subsalt gouge or rubble zone. Sufficient data for this analysis was obtained from 87 JIP wells. Statistical analysis of this large database allowed a wide range of correlations to be established for the subsalt rubble-zone occurrence with salt body structural and geological features. An early diagnostic of rubble zones using logging while drilling (LWD) tools can trigger certain drilling practices to be employed. This paper presents the diagnostic criteria for a subsalt rubble zone and several other confirmatory criteria. The diagnostic identification for a subsalt rubble zone is small-scale discordance between the gamma ray and the resistivity log in the interval immediately below the salt. The relationship between rubble-zone occurrence and salinity changes is discussed.Drilling subsalt rubble zones can be challenging. This paper documents current industry methods for drilling subsalt wells based on the analysis of multiple sources of data. In addition to the subsalt database, data was compiled from an industry questionnaire designed to capture current practices for drilling subsalt wells, a survey and reviews on subsalt drilling-related published literature, and personal interviews with industry professionals. This paper focuses on the following key subsalt (with and without a rubble zone) drilling issues of interest to wellconstruction professionals: the drilling window, casing setting, loss of circulation, wellbore stability, mud-weight scenarios, and leakoff tests. Highlights of each of the aforementioned drilling issues are presented along with well examples.

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Section: Rubble Zone Drilling Practices and Hazardsmentioning

confidence: 99%

Rubble Zone Below Salt: Identification and Best Drilling Practices

Saleh¹,

Williams

Rizvi

2013

Day 3 Wed, October 02, 2013

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“…In addition, Resistivity-based pore pressure prediction is dependent on many variables including: porosity, salinity, temperature, fluid type, saturation, shale content, type of clay, and texture. Resistivity changes resulting from changes of pore water salinity near salt masses may give a false indication of pore pressure changes (21,22). Based on the fact that generally rock compressibility has minor changes over a specific formation, a method for pore pressure prediction based on compressibility has been obtained which yields quite better results in carbonates (20).…”

Section: Introductionmentioning

confidence: 99%

A case study of challenges we have in pore pressure prediction techniques for a carbonate reservoir

Rashidi¹,

Marhamati

Bharadwaj

2015

2015 International Conference on Sustainable Mobility Applications, Renewables and Technology (SMART)

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Pore pressure prediction has always been a major challenge in the industry. Various attempts to predict pore pressure have been made by researchers to best describe the trend for a given region. Several methods have been published and claimed to work for many fields. This paper provides a case study for an oil field in Iran in order to check the applicability of some of the methods in this field.Eaton's, Holbrook's and Weakley's method are tried and it is found that Eaton's method provides a closer result,if not an accurate one. The details of the formation are stated to study the nature of these methods in such environment. The compaction exponent of Eaton's method is varied to see the variation in the trend for the field. The compaction exponent of 3.0 is found to work fairly well for depths up to 2600m while exponent value of 0.7 works for depth greater than 2600m. It is inferred that not all methods are applicable globally and there exists a need for further research to develop or modify these methods either qualitatively or quantitatively.

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