Evaluation of low resistivity beds using nuclear magnetic resonance log تقويم الطبقات الرملية منخفضة المقاومة الكهربية باستخدام تسجيلات الرنين المغناطيسي

Abstract

قد أثبتت طرق التسجيلات المستخدمة كفاءة مقبولة في مجال تقويم المكامن العادية ولكن عندما تعاني الطبقات المنتجة من انخفاض في المقاومة الكهربية تعجز تلك التسجيلات عن تقدير الخواص البتروفيزيقية وبالتالي تقويم المكامن تستطيع تسجيلات الرنين المغناطيسي حسابوبدقةالمسامية الفعلية ونوعية السوائل التي تشبع الطبقات ولذلك يعتبر الرنين المغناطيسي أداة ذات كفاءة عالية وعلى وجه الخصوص عندما تكون هناك إمكانية الاستخدام المشترك لتسجيلات الرنين المغناطيسي والمسامية والكهربية هذا البحث يوضح مدى الاستفادة من استخدام الرنين المغناطيسي في حل مشاكل الطبقات الحاملة للنفط ذات المقاومة الكهربية المنخفضة أو تلك التي لا تظهر تباينا كهربيا مع الطبقات المائية المجاورة

The combination of conventional logs such as density neutron and resistivity logs is proven to be very effective in the evaluation of normal reservoirs For low resistivity reservoirs however an accurate determination of the petrophysical parameters with the conventional logs is very difficult This paper presents some cases of low resistivity reservoirs and low contrast resistivity reservoirs where conventional logs fail to determine the petrophysical properties of formation The problems of these reservoirs are that conventional logging interpretation shows high water saturation zones but water free hydrocarbon would be produced In case of low resistivity contrast reservoirs it is difficult to determine oilwater contact with resistivity logs Nuclear magnetic resonance (NMR) log has been only available as a supplement tool to provide additional information on the producibility of the reservoirs The main limitations of NMR logging however has been the cost and long time of acquiring data This paper shows that in the case of low resistivity reservoirs NMR logging is a very effective tool which helps to accurately determine the reservoir rock petrophysical properties For the analysis of NMR data several aspects of NMR technique have been used ; 1) T1 T2 ratio for fluid identification 2) the difference between NMR derived porosity and total porosity to determine the types of clay minerals 3) NMR relaxation properties to identify fluids nature and rock properties of low contrast low resistivity reservoirs This paper presents three examples of low resistivity reservoirs Analysis of NMR data of low resistivity zones has helped to identify the producibility of these reservoirs zones to determine lithology independent porosity and to distinguish between bound and free water In case of low contrast resistivity reservoirs where there was little resistivity contrast between water bearing formation and oil bearing formation NMR has been able to identify the fluid nature of the two formations and then the height of the oil column This was based mainly on high contrast of NMR relaxation parameters