diff --git a/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.cpp b/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.cpp
index 372b7f2078..3fd1977ba6 100644
--- a/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.cpp
+++ b/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.cpp
@@ -182,6 +182,28 @@ void RigFemPartGrid::generateStructGridData()
         cvf::Vec3i ijk = m_ijkPrElement[elmIdx];
         m_elmIdxPrIJK.at(ijk[0], ijk[1],  ijk[2]) = elmIdx;
     }
+
+    // IJK bounding box
+    m_reservoirIJKBoundingBox.first = cvf::Vec3st(INT_MAX, INT_MAX, INT_MAX);
+    m_reservoirIJKBoundingBox.second = cvf::Vec3st(0, 0, 0);
+    cvf::Vec3st& min = m_reservoirIJKBoundingBox.first;
+    cvf::Vec3st& max = m_reservoirIJKBoundingBox.second;
+
+    for (int elmIdx = 0; elmIdx < m_femPart->elementCount(); ++elmIdx)
+    {
+        RigElementType elementType = m_femPart->elementType(elmIdx);
+        size_t i, j, k;
+        if (elementType == HEX8P && ijkFromCellIndex(elmIdx, &i, &j, &k))
+        {
+            if (i < min.x()) min.x() = i;
+            if (j < min.y()) min.y() = j;
+            if (k < min.z()) min.z() = k;
+            if (i > max.x()) max.x() = i;
+            if (j > max.y()) max.y() = j;
+            if (k > max.z()) max.z() = k;
+        }
+    }
+
 }
 
 //--------------------------------------------------------------------------------------------------
@@ -287,6 +309,14 @@ cvf::Vec3i RigFemPartGrid::findMainIJKFaces(int elementIndex) const
     return ijkMainFaceIndices;
 }
 
+//--------------------------------------------------------------------------------------------------
+/// 
+//--------------------------------------------------------------------------------------------------
+std::pair<cvf::Vec3st, cvf::Vec3st> RigFemPartGrid::reservoirIJKBoundingBox() const
+{
+    return m_reservoirIJKBoundingBox;
+}
+
 //--------------------------------------------------------------------------------------------------
 /// Find the face that is not perpFaceIdx or its opposite, and has normal closest to direction
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.h b/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.h
index 20e511c569..810f66015d 100644
--- a/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.h
+++ b/ApplicationCode/GeoMech/GeoMechDataModel/RigFemPartGrid.h
@@ -38,6 +38,8 @@ public:
     virtual size_t      gridPointCountK() const;
  
     cvf::Vec3i          findMainIJKFaces(int elementIndex) const;
+    
+    std::pair<cvf::Vec3st, cvf::Vec3st> reservoirIJKBoundingBox() const;
 
  private:
     void                generateStructGridData();
@@ -93,7 +95,7 @@ private: // Unused, Not implemented
     };
 
     IJKArray m_elmIdxPrIJK; 
-
+    std::pair<cvf::Vec3st, cvf::Vec3st> m_reservoirIJKBoundingBox;
 };
 
 
diff --git a/ApplicationCode/ProjectDataModel/RimGeoMechResultDefinition.cpp b/ApplicationCode/ProjectDataModel/RimGeoMechResultDefinition.cpp
index 26653e834d..ce0f48d30c 100644
--- a/ApplicationCode/ProjectDataModel/RimGeoMechResultDefinition.cpp
+++ b/ApplicationCode/ProjectDataModel/RimGeoMechResultDefinition.cpp
@@ -101,7 +101,7 @@ RimGeoMechResultDefinition::RimGeoMechResultDefinition(void)
     m_resultVariableUiField.uiCapability()->setUiEditorTypeName(caf::PdmUiListEditor::uiEditorTypeName());
     m_resultVariableUiField.uiCapability()->setUiLabelPosition(caf::PdmUiItemInfo::TOP);
 
-    CAF_PDM_InitField(&m_compactionRefLayerUiField, "CompactionRefLayerUi", 0, "Compaction Ref Layer", "", "The compaction is calculated with reference to this layer. Default layer is the topmost layer with POR", "");
+    CAF_PDM_InitField(&m_compactionRefLayerUiField, "CompactionRefLayerUi", RigFemResultAddress::NO_COMPACTION, "Compaction Ref Layer", "", "The compaction is calculated with reference to this layer. Default layer is the topmost layer with POR", "");
     m_compactionRefLayerUiField.xmlCapability()->setIOWritable(false);
     m_compactionRefLayerUiField.xmlCapability()->setIOReadable(false);
 
@@ -136,6 +136,11 @@ void RimGeoMechResultDefinition::defineUiOrdering(QString uiConfigName, caf::Pdm
     {
         caf::PdmUiGroup * compactionGroup = uiOrdering.addNewGroup("Compaction Options");
         compactionGroup->add(&m_compactionRefLayerUiField);
+
+        if (m_compactionRefLayerUiField == RigFemResultAddress::NO_COMPACTION)
+        {
+            m_compactionRefLayerUiField = (int)m_geomCase->geoMechData()->femParts()->part(0)->structGrid()->reservoirIJKBoundingBox().first.z();
+        }
     }
 
     if (!m_isChangedByField)