Use of Porosity as a Strength Indicator for Sand Production Evaluation

Abstract

Production history, fluid pressure and uniaxial compressive strength are basic data to evaluate the risk of sand production. Evaluations of the compressive strength based on logs are illustrated for the example of a well on the Germigny-sous-Coulombs structure. Then relationships between compressive strength and porosity are developed using a theoretical approach of grain contacts, the analysis of published rock mechanics data and mechanical measurements on plugs taken from well cores. It is shown that compaction factor can complement porosity in the analysis. A field example illustrates the relationship between a critical differential pressure and compaction factor or porosity. Introduction The general frame of this study is the production of oil and gas from poorly consolidated formations. It is well known that such a production can be hindered by the phenomenon of sand production. Various gravel-pack equipment can be used to prevent sand production but they are costly and generally harmful to well productivity. Therefore the decision to use such equipment has considerable economic impact and requires a clear-sighted evaluation of the risk of sand production. Tensile rupture and compressive rupture are proposed as possible mechanisms of sand failure. Tensile rupture is possible under two conditions:the fluid pressure gradient at the production face is larger than the gradient of the radial stress,the tangential effective stress does not exceed the level of compressive failure (less than ucs). As fluid pressure and tangential effective stress are linked through the equilibrium equation of the sand, conditions (a) and (b) impose an upper limitp max to the pressure difference Pd - Pw through the zone drained by a perforation. p max is proportional toucs and various values of the ratio p max/ ucs can be found depending on the drainage geometry (radial, spherical) and on the production history (influence of shut-in periods). Compressive rupture is also possible if, under symmetrical conditions: the pressure gradient remains smaller than the gradient of the radial stress, the effective tangential stress reaches theucs critical level. To these conditions corresponds a maximum of the total depletion ptd which depends linearly on ucs. The field observations apparently confirm the general trends of these theoretical analyses. For example satisfactory production conditions are obtained if the drawdown pressure Pdd is maintained under 0.5 ucs. Therefore using theoretical modelling and field observations two categories of data appear to be very important: pressure data characterizing the production history and the fluid flow as well as data characterizing the uniaxial compressive strength of the rock. P. 381^

Predicting rock mechanical properties of carbonates from wireline logs (A case study: Arab-D reservoir, Ghawar field, Saudi Arabia)

“…An alternative approach for estimating rock mechanical properties would be to use the porosity as the primary parameter. Sarda et al (1993), presented a direct correlation between the porosity (V) and uniaxial compressive strength (s UCS ): Farquhar et al (1994) derived a geomechanical index for carbonates that enabled rock mechanical properties to be estimated using general and field specific correlations. Edlmann et al (1998) used laboratory measured porosity and rock mechanical parameters for North Sea reservoirs to establish direct correlations between the porosity and the rock mechanical parameters and to produce continuous rock mechanical logs.…”

Principles of Drilling and Excavation

“…In ceramics with uniform grain size, laboratory measurements show that there is a correlation between UCS and porosity (f) (Sarda et al, 1993):…”

Evaluating Multiple Methods to Determine Porosity from Drilling Data

“…In this paper, three methods that have been previously published will be analyzed and compared to determine their accuracy and applicability to field data. These methods are: the Onyia method (Onyia 1988), Sarda method (Sarda et al 1993), Erfourth method (Erfourth et al 2005) and a new Gamma Ray method presented within this paper.…”