Bintulu is located 610 kilometres ( 380 mi ) northeast of Kuching 216 kilometres ( 134 mi ) northeast of Sibu , and 200 kilometres ( 120 mi ) southwest of Miri . Bintulu is located near the mouth of the Kemena River , in the coastal region of central Sarawak . Geology of the coastal area was formed during the Pleistocene period ; silt , clay , and gravel can be found here . Geological formation from the Oligocene period is found in the inland area , which contains limestone , siltstone , and sandstone . The soil is generally soft .