Changes

==Effects of organic matter on well logs==

==Effects of organic matter on well logs==

The increasing concentration of organic matter in a rock directly affects its properties by lowering density slowing sonic velocity increasing radioactivity raising resistivity and raising hydrogen and carbon contents. All of these attributes can be measured using density sonic, neutron, [[Basic open hole tools#Gamma ray|gamma ray]], and [[Basic open hole tools#Resistivity|resistivity logs]]. The table below (from <ref name=ch06r7 />) summarizes log responses to organic matter.

The increasing concentration of organic matter in a rock directly affects its properties by lowering density slowing sonic velocity increasing radioactivity raising resistivity and raising hydrogen and carbon contents. All of these attributes can be measured using density sonic, neutron, [[Basic open hole tools#Gamma ray|gamma ray]], and [[Basic open hole tools#Resistivity|resistivity logs]]. The table below<ref name=ch06r7 /> summarizes log responses to organic matter.

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! Log/Property

! Log/Property || Response/Value for Organic Matter (OM) || Comments

! Response/Value for Organic Matter (OM)

! Comments

|-

|-

| Gamma ray (GR) or uranium (U)

| Gamma ray (GR) or uranium (U) || High || High GR caused by U; can be linear with OM; U not always present

| High

| High GR caused by U; can be linear with OM; U not always present

|-

|-

| Density

| Density || Low (approx. 1 g/cm³ ) || Similar to pore fluids

| Low (approx. 1 g/cm³ )

| Similar to pore fluids

|-

|-

| Neutron

| Neutron || High || Due to hydrogen in OM

| High

| Due to hydrogen in OM

|-

|-

| Sonic

| Sonic || High transit time || Estimates vary from 150 to more than 200 μsec/ft

| High transit time

| Estimates vary from 150 to more than 200 μsec/ft

|-

|-

| Resistivity

| Resistivity || High || May not affect log response unless generated hydrocarbons occupy pores

| High

| May not affect log response unless generated hydrocarbons occupy pores

|-

|-

| Pulsed neutron

| Pulsed neutron || High carbon-oxygen ratio || Most direct measurement of carbon; needs inorganic correction

| High carbon-oxygen ratio

| Most direct measurement of carbon; needs inorganic correction

|}

|}